Follow Slashdot stories on Twitter

 



Forgot your password?
typodupeerror

Comment: Re:Mint 15 (Score 2) 270

by fnj (#49611911) Attached to: Ubuntu 15.04 Received Well By Linux Community

'sudo bash' and 'sudo -su root' do the same thing.

Wrong, genius. See which one runs /root/.bash_profile and which one doesn't. See which one gets PATH set to root's path and which one doesn't. Neither of yours does.

sudo -i is probably the command you are reaching for. Very similar to sudo su -. Whichever one you are comfortable with. They both do a true root login.

Comment: Re:Another market overlooked (Score 1) 293

by fnj (#49610041) Attached to: Tesla's Household Battery: Costs, Prices, and Tradeoffs

The outages that only last a couple of hours are nothing more than a nuisance. When it starts reaching a day or more, it becomes a goddam nightmare. Without the well pump, you have no running water. Without water, you cannot flush the toilet. The refrigerator contents start to spoil. In the winter you have no heat. Residual water in the pipes can burst.

I would be perfectly happy with just the essentials. Well pump, furnace, and refrigerator. A 2 kW source with enough surge for motor starts would be enough. Not sure if 7-10 kWh would be enough to cover 2-3 days. You can manage the well pump by planning your use for brief periods of running; it has a very low duty cycle most of the time anyway, even in normal use. You can manage the furnace to an extent by building up a lot of heat and then letting it coast down for hours. The one you can't really manage is the refrigerator. But overall, this looks promising. It would be a lot more practical than a generator where you have no natural gas hookup.

Right up until I learned it does not include an inverter. WTF? My eyes rolled up in my head and I groaned. Shit. How stupid can you get with your marketing? OK, you also need changeover provisions. So maybe this is the province of a specialized reseller. Until I hear from one of those and hear the bad news on the bottom line, I am utterly unimpressed.

Comment: Re:Price won't come down (Score 1) 293

by fnj (#49609951) Attached to: Tesla's Household Battery: Costs, Prices, and Tradeoffs

Likewise, lithium from seawater is not economical

Says who? About one screen above your message we are informed that getting enough lithium for a Tesla Model S from seawater would cost $500, compared to $150 when mined. Altering the Tesla price from $79,900 to $80,250 sure as hell wouldn't make the latter any more uneconomical than the former.

A cellphone battery is very roughly 1/10,000 of the pack in a Tesla. Adding 35 cents to the cost of a $300-$800 cellphone certainly wouldn't make it uneconomical.

Only a tiny part of the expense of a lithium ion battery is the cost of the lithium.

Comment: Re:Most electric cars are powered by burning coal (Score 1) 279

by fnj (#49587495) Attached to: New Study Suggests Flying Is Greener Than Driving

Electric traction motors are far more efficient than ICEs. That's why diesel locomotives don't actually connect the diesel engine to the wheels.

You are high. The diesel engine turns fuel into mechanical energy. If you change that mechanical energy into electricity and then back into mechanical energy, there is no way that could give you more efficiency than a simple mechanical transmission (which is typically well over 90% efficient). The reason for the electric transmission is flexibility. It does away with a big honking clutch and a multi-speed gearbox and gives you very smooth transition from standstill to forward motion.

Comment: Re:Masstransit is more energy efficient than perso (Score 1) 279

by fnj (#49587273) Attached to: New Study Suggests Flying Is Greener Than Driving

Any combustion engine running at surface conditions can do maybe 20 - 30% efficiency tops.

Better than that. There are internal combustion engines which reach 50% at sea level. The Wartsila-Sulzer RTA96-C 108,920 hp marine diesel exceeds 50%. Heck, even the TDI diesel engine in my 1999 Golf tops out at very close to 40%. The LM-2500+ gas turbine, a derivative of the CF6 which powers some 747s, adapted for shaft output, is over 39%.

Testing can show the presense of bugs, but not their absence. -- Dijkstra

Working...