hatcravat · HackerTrans

13 ปีที่แล้วdiscuss

Who cares about the efficiency when solar panels weigh over 50 kg per kW? Even at SpaceX prices, the cost of launching a solar panel into space is hundreds of times the cost of the panel. If your alternatives are "buy 500 panels and put them on the ground" and "buy one panel and put it in space," why the hell is anyone even remotely considering the second option?

hatcravat

13 ปีที่แล้วdiscuss

Did they? It sounds like they had access to confidential Apple documents, which allowed them to rewrite their patent in a way to make it look like Apple infringed on technology they invented. Remember, the point of a patent is to disclose new inventions.

hatcravat

13 ปีที่แล้วdiscuss

Yes, but how are they going to do that if they can't see the drone? How will they know when they have succeeded? Are they just going to continue driving recklessly until they run out of gas?

Driving evasively seems like a very good way to attract the attention of other officers who might not recognize the suspects' car. Once the cruiser is out of sight, the suspects' best bet would be to "act casual." If the drone can see the suspects then it doesn't matter how they drive, and if it can't see them then driving like a maniac only makes it easier to be found.

hatcravat

13 ปีที่แล้วdiscuss

Following this train of thought to its logical conclusion: Without children's entertainment, kids would be forced to read free books from the library or go play outside. The horror!

Look, shared cultural nostalgia is great, and all, but I'm not sure that makes for a good reason to allow advertizing to kids.

hatcravat

13 ปีที่แล้วdiscuss

Doppler shift due to observer speed will almost always (i.e. for anything other than an actual ballistic missile, and even then only a missile traveling west) be less than the doppler shift due to satellite speed for a stationary observer. So, artificially restricting the doppler spread isn't an effective method of implementing the COCOM restrictions. It would also make PLL lock-up more difficult.

Concorde is old enough that its operators probably never went to the trouble of doing the paperwork to have a GPS integrated with the rest of the NAV system. For its (relatively) short flights, an internal navigation system plus VHF or LF radionav works adequately (and there were very few, if any, GPS/WAAS approaches certified by the time of its retirement).

hatcravat

13 ปีที่แล้วdiscuss

Small generators rarely have emissions control systems anywhere near as good as the main engine (and it most cases, far worse). They usually have a completely open-loop fuel mixture control: a carburetor set to provide an adequate air/fuel ratio when the fuel tank is half full.

So, saying that only the generator is running isn't a very effective way to argue that these trucks are low-polluting.

hatcravat

13 ปีที่แล้วdiscuss

Actually, Steve Mann was doing this fifteen years ago. There are web pages describing his wearables that literally haven't been updated for a decade. Think about that for a second. Bill Clinton was president when this was cutting edge stuff. And the Glass hardware looks just as stupid and dorky as the hardware Mann built himself.

hatcravat

13 ปีที่แล้วdiscuss

No. This is wrong. First, sampling need not imply quantization[1]. Second, the signal to noise ratio of the continuous signal source is important. With sufficiently many bits and sufficiently many samples, you can exactly reproduce any band-limited continuous signal above the noise floor[2]. Those last four words are important. Analog data never comes without noise, and a "sufficient number of bits" is nowhere near as high as you think (particularly with noise-shaping techniques like dithering).

Now, it is the case, as user rayiner mentioned, that there can be advantages to using more than the required number of bits and samples (though not quite for the reasons he mentioned). For starters, you do need an anti-aliasing filter between the signal source and your ADC. Increasing the sample rate reduces the complexity of the AA filter, and digital-domain math can make up for it (and increase the effective number of bits, to boot!). But when you go to reproduce the signal, there's no good reason to use more samples and bits than necessary. That was the whole point of the "Niel Young paper" that has been linked to so many times.

Vinyl does not come close to the limits of consumer-grade recording devices (except maaaaaybe in certain bands, but that can be dealt with by using noise-shaping techniques). Does that make those who like the sound of vinyl bad people? No. Just like those who enjoy sitting in front of a wood fireplace are not bad people. Gas fireplaces have a lot of advantages, but some people like the crackling of the wood and the smell it produces.

[1] Tektronix made a very nice set of (entirely analog) sampling oscilloscopes in the 1960's which used sampling techniques to measure high frequency signals (on the order of 1GHz when contemporary continuous-signal CROs could barely reach 100MHz). These oscilloscopes displayed discrete-time, continuous-amplitude signals, and deliberately excluded the anti-aliasing filter I mentioned above (though it wasn't true heterodyning as most RF people would think of it, because samples were taken based a delay from a trigger recognizer, and thus not necessarily equally spaced in time).

[2] Signals below the noise floor are outside the scope of this discussion and usually require some form of synchronous detection (like a lock-in amplifier) or frequency-spreading / -despreading (like GPS).

hatcravat

13 ปีที่แล้วdiscuss

>they convinced the labels to stop requiring it.

Are you sure it wasn't the other way around? People were building huge libraries of music that only worked on Apple products (iPods and iTunes) around the time the labels allowed Amazon to start selling DRM-free MP3s. Apple would have gained an enormous amount of leverage if the labels had allowed that to continue: "Oh, you won't accept our terms? Well, then your product won't be playable on 90% [0] of portable music devices [1] and won't be available in the largest online music store (and your competitors' will be)! I hope not all your artists have left by next fiscal quarter." For all he talked amount it, I'm not convinced that Steve Jobs ever wanted to see the iTunes Music Store go DRM-free.

The market penetration of iPods meant that only path forward for the labels was one that allowed people to listen to music on their iPods. The only way to do that was selling DRM-free MP3s or protected AAC files. As a bonus, DRM-free MP3s worked on all the cheap flash-based players (which always had greater deployment than any of the DRM-compatible players from Sony and Microsoft).

[0] A number generated by my PRNG (posterior random number generator). But the iPod Classic really does have an absurd share of the >64GB market (probably declining now that you can get tablets and phones with 128GB of flash). [1] Don't forget that Apple has only ever supported their own DRM. Protected AAC files play on Apple devices and only Apple devices. Apple devices support only protected AAC and DRM-free formats.

hatcravat

13 ปีที่แล้วdiscuss

> Also - does he really have so much experience with that tech?

Well, I, for one, was fascinated with wearable computers for a time after reading an article about Steve Mann (in MIT Technology Review, IIRC). That was about fifteen years ago. Based on my memory of that article, I'd say that 20 years is a bit of an understatement.

hatcravat

13 ปีที่แล้วdiscuss

I too think this is a very exciting sub-field. EMTs and the like already have something like this, only better: It's called a pulse oximeter, and it determines both heart rate and blood oxygen saturation by measuring the absorption ratio of two wavelengths of light. Commercial devices clip on your finger and cost about $50 (the whole device is about the size of two fingers).

hatcravat

13 ปีที่แล้วdiscuss

> I don't 100% get the band limited signal bit. How does band limiting imply that there's only a single possible reconstruction of the digital signal? I can kind of picture the fourier transform meaning that there's only one representation but it's a bit of a leap for me. Can the converter itself not create the signal incorrectly?

Nyquist's theorem shows that you can reproduce a sine-wave, provided that you have strictly greater than two samples per cycle (and implicitly assume that you have a sine wave).

Any periodic signal (which, for audio, which is AC-coupled, is always) can be represented exactly by it's Fourier transform. The FT is simply a different representation of the same function, namely a sum of sine-waves. In general the FT of a signal has many terms (i.e., many spectral components or harmonics). However, in a band-limited system, only certain harmonics are allowed to pass. If your audio system claims to have, say, 20Hz to 20kHz bandwidth, then any Fourier component outside that range will be greatly attenuated (if the attenuation puts that component below the noise floor, we could say that the component has been completely eliminated). It is the act of attenuating those out-of-band components that causes the square wave to go squiggly.

This means that for any arbitrary signal which has been band-limited to half your sampling frequency, you can exactly reproduce the band-limited copy.

The sampling system usually (for consumer audio, always) has an anti-aliasing filter between the signal source and the sampler (not having an AA-filter is what allowed Tektronix sampling oscilloscopes to show multi-GHz signals in the 1960's, by effectively heterodyning the signal frequency down to something usable). That means that the digitizer only ever sees the band-limited signal. The bandwidth of the AA-filter is chosen so that the maximum frequency passed to the sampler is half (or less) than the sampling rate.

This also might help: http://dsp.stackexchange.com/questions/7879/how-does-subpixe...

> Isn't there also an argument that frequencies above 19khz can be heard by some people so need to be accurately represented?

That argument has been put forward, yes. "Back in the day" Bell Labs performed actual experiments with human test subjects to produce "equal loudness" curves. The upshot is that the power of an audio source must increase as the fundamental tone rises (starting from about 4kHz, or so). Then you must consider the effect of loud sounds on the human ear. Hearing damage is cumulative and the rate of damage increases with sound power, so it's hard to put an exact upper bound on the upper power limit of human hearing. However, at some point in the 18kHz to 22kHz range, the equal loudness curve crosses the damage curve. At that point you have to turn up the power of the audio source so high that you damage your hearing listening to it: So there is a definite upper frequency limit to human hearing. It may be slightly higher for some people than others, but 22.05kHz (the Nyquist limit for CD-rate sampling) is almost certainly greater than many standard deviations above the mean.

It's difficult to admit for a group of people (engineers and scientists) who are always striving to make things better, but we have come to a point where audio reproduction is "good enough." For a modest amount of money, the sampling, storage and reproduction is for all intents and purposes "perfect." Your living room is never going to sound like a concert hall with a live orchestra, but it's not because you don't have enough bits or samples or bandwidth.

hatcravat

13 ปีที่แล้วdiscuss

The overnight stop is really a red herring: The battery only lost about 5-7% of capacity overnight, which is much less than the difference between a standard charge (90% of capacity) and how much the Times charged the battery (72%). Actually, it's too bad CNN didn't stop someplace for the night just to prove this.

hatcravat

13 ปีที่แล้วdiscuss

I speculate that it is a interaction of several things:

1) The current firmware assumes there is "unlimited" energy available when charging, so it can keep the battery warm with little impact on charging rate (this is not a bad assumption for everything other than 120V/15A charging).

2) The current firmware assumes that the battery needs to be kept warm when charging (this is not a bad assumption for everything other than 120V/15A charging, but may not be correct for low-power charging).

3) The power required to keep the battery warm in near-zero (Fahrenheit) temperatures is nearly the same as the maximum continuous power available from a 120V/15A outlet (1.44kW, because the maximum continuous load is only 80% of the maximum load), at least initially.

The firmware probably needs to be tweaked for cold-weather, low-power charging. The firmware needs to know how to estimate state of charge when the battery is colder than normal. It could probably prioritize charging ahead of heating until the battery reaches a higher state of charge.

hatcravat

13 ปีที่แล้วdiscuss

You could always rent a vehicle for your remaining driving needs. For 10% of total driving that might be somewhat impractical, but 10% sounds like a pretty high estimate for trips that would challenge the Model S's range. That's one long-range trip every week and a half. Yes, there are people who drive like that, but they are very much in the minority.

If you drive to grandma's/the in-laws/"up to the cabin" three or four times a year, that's only 1% of trips (assuming you commute every day and run local errands on the weekends). Most families in the US already have multiple vehicles. Why can't one be an electric?

hatcravat

13 ปีที่แล้วdiscuss

I'm not sure why you bring up Classic, Carbon, or PowerPC. Rosetta was dropped from Lion (two releases ago) and support for Classic was dropped when Rosetta was added. MS Office 2008 (I think it was) stopped working with OS X Lion (2011) because the installer executable contained PPC code. Not very many people need or expect 30 years of backwards compatibility. They just want more than 3.

hatcravat

14 ปีที่แล้วdiscuss

Actually, I think you misunderstand the analogy. The color of the middle wire on the distributor is something you'd like a prospective mechanic to know, so he isn't learning on your time. It isn't, however, something that is in any way relevant to driving a car. I think this is why your comment provoked such hostile responses.

The programmer equivalent of the middle wire color question is something like, "Is the 3-phase power supply on XYZ mainframe wired in a delta or wye configuration? As a followup, what is the input frequency tolerance?" A sysadmin might need to know that, and an electrician certainly would, but it is far, far outside the purview of a programmer. [Edit: I'm assuming the programmer to be someone writing software running on the mainframe, not the firmware for a microcontroller in the power supply]

Maybe you're just a very good interviewer and haven't had to deal with the 90% that are crap? :+)

hatcravat

14 ปีที่แล้วdiscuss

Regarding point 2, the article gave me the impression that they used historical measurements of the the mains frequency as part of the analysis. Since Britain is on a single grid, the local conditions shouldn't affect the recorded signal. I'm sure it is possible to find patterns (frequency drops slightly in the morning as the public utility tries to keep up with increasing demand), but you wouldn't know, for example that the utility overestimated demand on the particular morning that the audio was alleged to have been recorded (and thus that the frequency was actually higher).

As for point 1, there are a number of plausible angles to approach this, but I think that the forensic adversary has a huge advantage: Synchronous detection. The approximate time of the recording is known, as is the historical record of mains frequency. That allows for the possibility of huge processing gain, which might allow for recovery even after the amplitude of the mains hum is filtered to below the quanta of the audio system. I almost think you might have to Fourier Transform the whole audio record and zero out any component at f_mains +/- delta (and harmonics). That, of course, would look pretty suspicious to a forensic analyst.

Even that might not be enough if mains hum has a determinable effect on the data compression algorithm used to store the audio data.

Edit: The point I was trying to make in the first paragraph is that if you wanted to forge a recording, you'd need to have the grid frequency data. Having it for anywhere would be good enough and not having it for anywhere simply wouldn't.

hatcravat

14 ปีที่แล้วdiscuss

Well, you're right: It is 2012, and there are (at the time of writing) all of 6 supercharger stations, which can fill a battery at up to 120 kW. The current incarnation (heh) of the Tesla S battery limits the rate to about 80 kW for the first 50%, or so.

However, there are probably more places to plug in than you'd expect. For example, there are tons of RV parks all around the country, many of which have NEMA 14-50 sockets for grandma and grandpa to plug their big camper into. Those sockets can deliver about 10 kW. Then there are electric clothes dryers, found in many homes: They typically use a 240V, 30A circuit, which can deliver about 5 kW continuously.

That last option isn't really practical on the freeway, but how far do you plan to drive to hang out with friends for half an hour? Let's say you drive a couple hours and stay for the afternoon: Their dryer socket will refill almost half of a Tesla's battery for the grand sum of $5--that'll be enough to get you home (there are practical problems with the approach, but it's not a bad 0th-order approximation). Are your friends so worried about electricity that they wouldn't accept a 6-pack of their favorite brew in exchange for a power outlet?

Electric car owners who frequent online forums report that hotels are very reasonable about charging, and some even install free-to-use chargers as a value-add to attract customers. In the long term, if electric car adoption increases, hotels will obviously either need to add a surcharge or raise room rates. But, even if a hotel did sell electricity at a 100% markup, the customer's energy cost for driving a mile on electricity would still be less than half the cost on gasoline.

Certainly, electric cars won't work for all trips, and the infrastructure needed to move electrons from the grid to the car is missing in many places. On the other hand, equipment for 10 kW charging (that's a charge rate of about 30 miles per hour) can be installed almost anywhere in the continental United States for between a few hundred and couple thousand dollars (and in many places it already exists). For new construction, before landscaping is installed and where a right-size breaker panel can be installed in the first place, the cost of installing 240V, 50A service in the garage is almost inconsequential.

hatcravat

14 ปีที่แล้วdiscuss

I think part of the problem is also that many people underestimate the amount of time it takes to stop for gas. For city driving, you start with a full battery in the morning and never worry about stopping for gas (so the only place charge time matters is on the freeway).

The amount of time spent actually transferring liquid into the tank may only be 5 minutes. But then you need to add the time it takes for your card to authorize, the time it takes to go inside to use the restroom and buy snacks, etc. Then there's time it takes to get on and off the freeway (it always seems like there's a red light at the end of the off-ramp and another one to get out of the gas station). If you stop for fast food, that adds another 10 minutes (30 for a sit-down restaurant). Someone is sure to chime in that a gas car with three drivers and an empty container can drive 23.5 hours per day: I'm sure we've all done that at least once in college, but that mode of transport is much less appealing after one grows up.

My point is just that when all is said and done, the comparison is less like 5 minutes vs. 30 minutes and more like to 25-40 minutes vs. 40-50 minutes. The electric is still slower, but not 6 times slower, and you have an excuse to eat slightly less unhealthy food.

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