HNHacker News
TopNewBestAskShowJobs

sfasfsafd

17 karma · joined May 24, 2019

submissionscomments
sfasfsafd··on Lessons from cold fusion, 30 years on
It's a partly a problem of semantics, really. You can't really say it's a fusor runs at >45K because you're not in thermodynamic eq. (and therefore, there is no T).

Likewise a laser runs at "negative" T, but which is hotter than infinity T (pop inversion happens at T<0). There's no contradiction because T is again defined in eq., so we're just abusing terms.

So if we got net energy out of a fusor it would, for all practical purposes, be "cold" fusion. In fact, it doesn't have a T at all ;)

sfasfsafd··on Uber will start deactivating riders with low ratings
If the driver has snow tires, they're a safer driver than one with all-weather and a blank dash.
sfasfsafd··on Uber will start deactivating riders with low ratings
"TPMS sensor light is on (major safety risk)"

It really isn't. (very) low tire pressure is a major safety risk. The TPMS sensors I've had all seem to go off at minor deviations (few psi) from the tire pressure; deviations that aren't a safety risk.

A useful reminder that the winter is coming, but hardly a major safety risk.

sfasfsafd··on If the number of children is not growing, why is the population still increasing
"introduce small quantities" small being the key qualifier.
sfasfsafd··on Superconductivity near room temperature
Also, super conductors are limited by the amount of magnetic field, and therefore current they can carry [0] (above that limit they become normal conductors). Lowering T bellow Tc, increasing P increases the amount of current you can carry.

Point is, they're kinda useless for transmission.

[0] MRI magnets are superconducting for the efficiency of superconductors, not for the field strength! The strongest magnets are not made of superconductors but out of copper pipes: electrical conductors with coolant pumped through them!

sfasfsafd··on Superconductivity near room temperature
Ya, but the science popularizers always make it about transmission :S
sfasfsafd··on Superconductivity near room temperature
Insignificant: EEs can lower the losses by increasing the line voltage [0], at the expense of other challenges (namely taller pylons). It's about 5% over the length of the line.

Consider the other losses:

- Thermal (gas turbine) cycle: 40-60% lost (the big one) - Transformer loss: 1-2%. You pay this every time you step up/down, so it adds up. - Capacitive coupling: I dunno, but length dependent. It has to be about the same as Ohmic losses since once it's large you switch to DC lines (and take an Ohmic loss hit from lower V) - You're house's power factor (which, unlike industrial users, you're not charged for).

[0] in the sixties very large V lines were introduced (0.75 - 1.0 MV ??). They work, but it's not considered worthwhile.

sfasfsafd··on Superconductivity near room temperature
"well the pressure aspect wouldn't require constant energy input."

But you have to put energy in to compress it, energy that is lost (since you're compressing it isothermally). Since we're talking about 1E6 atm, any appreciable volume would require insane amounts of E to compress.

sfasfsafd··on Superconductivity near room temperature
at a 1E6 atm, it's beyond useless for any practical application (unlike "normal" superconductors that can be used with a bit of N2 plumbing). If you scroll through the paper, you'll see they talk about using a diamond anvil.

Even if we could compress anything other than a spec of this stuff, it would still require massive amounts of PV work to achieve the P required.