87 karma · joined June 22, 2012
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.
Look, shared cultural nostalgia is great, and all, but I'm not sure that makes for a good reason to allow advertizing to kids.
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).
So, saying that only the generator is running isn't a very effective way to argue that these trucks are low-polluting.
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).
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.
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.
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.
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.
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?
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? :+)
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.
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.
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.
LibreOffice works just find for my word-processing needs.
Edit: Forgot about Gnumeric for a moment. It's probably twice as good as LibreOffice for what I need, but doesn't do 100% of what Excel does.
Part of the reason you see so much backlash from teacher's unions against these initiatives (despite the fact that virtually all teachers acknowledge that some are better than others, and have a pretty fair idea who the worst ones are) is that they don't see this as a way to fairly evaluate teachers and improve the quality of education. Rather, they see it as a weapon to be wielded by school districts, school administrators, and angry parents ("Mrs. X told little Johnny (age: 17) where babies come from!" "Mr. Y is a member of $MARGINALIZED_SUBGROUP!" "Ms. Z believes something that is the current scientific consensus" "Mr. Q gave my son an A-") against unpopular teachers. It is an unfortunate fact of life, and even more unfortunate that so few are willing to admit it (especially here on HN, where the quality of discussion is usually above average).
We would probably have much greater buy-in from teaching unions if these evaluations were perceived as something other than politics as usual. Unfortunately, the proposals all seem to keep a some level of human involvement in the firing process (so only the very most outstanding teachers are immune to the usual political pressures). It's useful at this point to recall a bit of history: Teachers today are so hard to fire because they have tenure. Teaching unions successfully forced tenure the tenure system on school districts because school administrators of the past abused their authority to fire good teachers who happened to be politically unpopular.
I'll explain anyway: Many countries have some sort of passport control both when you enter and when you leave the country. The reasons for this are varied, but a common one is to make sure you didn't overstay your visa. As a result, you need to have a valid visa attached to your passport to pass through passportcontrol to exit the country. It is almost never sufficient to have been issued a visa to pass through passport control. You almost always need the one physical piece of paper that is the physical manifestation of the visa.
If your employer has your passport, they also have the visa which was stapled to it. Your embassy can easily get you a replacement passport, but a replacement visa is up to the host country.
Your two options to leave are: 1) Ask your former employer for your passport and visa. 2) Go through some (or a lot, to judge from the other comments) bureaucracy to get a new visa.
The processor on this chip is an ARM cpu with floating point support, probably not something that most would consider exceptional. But for a microcontroller like this, the most interesting aspect is the on-board peripherals. Most MCUs will have some sort of analog to digital converters, counter/timer blocks, etc. You can download the datasheet for the Stellaris chip in question from here: http://www.ti.com/lit/gpn/lm4f120h5qr
Some of the highlights: 12 counter/timer blocks. They each have a capture/compare block which can be used, e.g., to measure timing of external events or output a PWM train (for digital to analog conversion). The timers can also trigger the start of a DMA transfer or the start of an analog conversion.
A 1 million sample per second A to D converter with 12 bit resolution. The ADC has hardware decimation support (up to 64 samples), which can be used to trade off sample rate for sample resolution. The converter also has a 12 channel input multiplexer. Also, unlike the ADC in your sound card, this has DC-coupled input, so there's no lower cut-off frequency.
A DMA controller with support for scatter-gather modes. Transfers can be triggered by the completion of an A/D conversion, the comparators, the timers, or by software.
Two analog comparators: The comparator output can be used internally to trigger interrupts or start a conversion on the ADC.
*There are 8 UARTs, 4 synchronous serial ports, and one each I2C, CAN, and USB controller. So you can talk to a lot of peripheral devices. The UARTs support rates as high as 5 Mbps.
So, what do you want to do with these building blocks? It's kind of up to you. One application I can imagine is a substantially less-sucky (compared to all the other ones out there based on MCUs) audio-frequency oscilloscope. The ADC sample rate is almost high enough to support it, particularly if you designed a decent front-end, and the analog comparators could be used to do interesting things with triggering (lots of MCUs try to fake it, badly, with software triggering).