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Comment Re:Why (Score 1) 201

Adiabatic compressed air energy moves the heat from compression into an insulated thermal mass chamber, and uses that to heat the expansion vessel. It recouperates that loss and has 70% total effective energy storage--higher is possible, up to 90%.

The way you describe it sounds not at all like an adiabatic (no heat exchange) process but rather like a thermodynamically irreversible process. Maybe you mean an isothermal process?

And from :
"real compressors and turbines are not isentropic, but instead have an isentropic efficiency of around 85%, with the result that round-trip storage efficiency for adiabatic systems is also considerably less than perfect."

Wikipedia doesn't say so much about isothermal compression in practice, but it sounds to me like practically infeasible to reach your 70-90% roundtrip efficiency. You'd need an enormous thermal mass that doesn't change much in temperature despite 1/3 or so of the energy being stored as heat, you need enormous heat exchangers to transfer the heat with negligible temperature differences, and your compressors and decompressors need to have a very high efficiency.

Comment Re:What bugs me about USB power (Score 1) 152

IMHO: A USB device that depends on its power source to limit its input current, and can be damaged by a host that is willing to deliver more current that it requested, is defective by design.

Current limiting is to protect the supplier of the current. Bad current negotiation can damage the power supply, so of course the power supply should limit the current. A bad power supply may break, though. I think the main problem is that USB-C can use a range of voltages and a 5 V device plugged into a 20 V power supply will blow up the device unless the 20 V supply is signaled to throttle back to 5 V.

But maybe I misunderstand. Unfortunately, the reporting about this topic (Leung's findings) is very fuzzy about what happens exactly. But I don't see any scenario where connecting a good quality 5V, 1A or 2A charger to any USB-C device can lead to damage.

Comment Re:I Stopped Using Custom ROMs (Score 1) 215

"your uncommon hardware may get burned out early (I've lost many wifi / gps / bluetooth / 3g-4g chipsets that way)."

This is the first time I hear smt like this. Do you have evidence?

The gps radio in my nexus 5 (with CM) tends to deteriorate over the months, but it turned out that tightening the screws of the rf shield restores the reception. Not a software issue.

Submission + - WhatsApp encryption back door ( 1

siloko writes: From the article: "A security backdoor that can be used to allow Facebook and others to intercept and read encrypted messages has been found within its WhatsApp messaging service."

Comment Re:Is this theoretical? (Score 1) 207

A modern dac is supposed to digitally filter at 20 kHz (very hard cutoff), in exchange for lots of noise above 100 kHz. A soft roll-off analog filter takes care of the content above 100 kHz.

I suspect that ultrasound in this context really means 16 kHz or so, at volumes that are too low for the ear, but easily picked up by a microohone and some signal processing.

Comment Re:Is this theoretical? (Score 1) 207

What kind of audio source did you use to find that you can hear 22 kHz? Unless you have an ultra low noise analog sine wave generator and amplifier, you are likely to hear noise, artifacts of the DA converter, and effects of clipping when you crank up the volume. The stated limit of 20 kHz for the human ear is the frequency where the pain threshold and the hearing threshold coincide for an average young person, so it is likely that you need >110 dB SPL to have any chance of hearing above 20 kHz. A device with 90 dB S/N ratio will likely blast you with lower frequencies, which you could easily mistake for "I can hear 20+ kHz".

I did once fry the tweeters of my (60 watt rated) loudspeakers while trying to test the limits of my hearing as I was sending all amplifier output power to the tweeters.

Comment Re:Battery life is not the real issue (Score 1) 254

Although the general point is probably correct that min/max charge levels affect Li-ion lifespan, I would be careful with using batteryuniversity as a source of information. It's really a weblog of a small manufacturer of battery chargers that presents a couple of small-scale test results as if they represent the absolute truth for all brands and types of Li-ion batteties.

Comment Re:T-mobile appealing, continuing practice (Score 1) 61

Until a music-streaming provider complains about being discriminated against, I don't think the review of the whitelist is the problem. The legal issue seems to be about the question whether discrimination by type of content (music, in this case), regardless of the company that provides the content, is allowed or not.

My feeling is that T-mobile is in a weak position here. Because if T-mobile is right, they would also be allowed to discriminate against other types of content; for example by making VoIP traffic more expensive. In fact, this is already happening: the cost of any data traffic is increased to subsidize the bandwidth for music data.

Comment T-mobile appealing, continuing practice (Score 2) 61

Spotify, mentioned in the summary, is a bad example, since it is one of the many streaming services that is whitelisted. T-mobile allows any streaming provider such as spotify to sign up, without restriction or charges. According to T-mobile, this is allowed by the European law, which takes precedence over Dutch law. So, they are appealing in court and continuing their service for the time being.

References (Dutch, you'll have to pass it through Google Translate):

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