Volvo is introducing a 112mph speed limiter to all its new cars - <AUTHOR> https://arstechnica.com/cars/2019/03/from-2020-volvo-will-limit-all-its-new-cars-to-112mph/ <comment><USER2> There is no circumstances under which a maximum speed of 112 would bother me. I drive a Honda Fit. I don't think I have ever driven it over 85 miles per hour (137km/hr). I'm not comfortable driving faster than that. What makes me mad is that my speedometer goes up to 140mph! Why?! The only answer I've ever seen that makes sense is that it's a marketing tool, but who honestly buys a Honda Fit and thinks to themselves "if this thing can't do 140 then forget it!" The downside is that it's actually very hard for me to tell exactly how fast I'm going because in general I'm driving less than 60mph in my daily commute and yet that range is only 43% of my analog speedometer. I honestly wish it only went up to 100mph, then I'd be using 60% of the resolution of the dial. Instead I have no idea whether I'm going 35 or 40 unless I really stare at the thing :(

<comment><USER3> I drive a 392 challenger scat pack shaker... I don't think I've ever had it over 100, though the max is 201. I'm not sure I'd be bothered by a regulator for the top speed.

That said, I don't think speeding is even close to the number 1 killer these days... Cell phones seem to be the leading cause of accidents these days. Maybe they should detect motion over 5mph and turn off display of messaging apps, only bluetooth voice interactions allowed.

<comment><USER4> > I drive a 392 challenger scat pack shaker... I don't think I've ever had it > over 100

I don't see the point of a vehicle like this unless you drag race it on a regular basis. It has limited utility, is larger than an Abrams tank, guzzles fuel like it's 1998 and couldn't make it around a slalom cone course even with a skilled driver. It's a make a lot of noise and go really fast in a straight line car. That's what it does (nothing wrong with that).

<comment><USER5> it's fun to drive

entertainment has value to some people

<comment><USER4> I get it (I'm an amateur race car driver). What I'm saying is, OP is not using the car to it's full potential.

<comment><USER6> Most people don't use things to their full potential. We have cars with larger engines than needed, CPUs and memory banks that rarely stay above 90%, food that gets tossed out daily, laundry washed and dried at half capacity and below, and so on. Many developed nations would look differently if we used everything to their full potential potential.

</comment></comment></comment></comment></comment></comment><comment><USER7> In the past 2 years, Volvo discontinued all engines with more than 4 cylinders [1], announced that all future cars would be HEV or EV [2], then declared that the current ICEs would not be developed further.

Other car companies make a few innovative models, but (apart from Tesla) I don't know any other companies which have made sweeping statements about every model they'll ever make. I think Volvo has the strongest brand today, in the sense that I know what they stand for. They've come a long way from "boxy but good".

[1]: [https://www.seattletimes.com/business/volvo-xc60-moves-to- al...](https://www.seattletimes.com/business/volvo-xc60-moves-to- all-4-cylinder-engines/) [2]: [https://www.caranddriver.com/news/a15340510/volvo- electrifyi...](https://www.caranddriver.com/news/a15340510/volvo-electrifying- entire-lineup-in-2019-but-gas-isnt-dead/) [3]: [https://www.caranddriver.com/news/a18725989/driving-on-e- cur...](https://www.caranddriver.com/news/a18725989/driving-on-e-current- volvo-engines-will-be-the-companys-last/)

</comment><comment><USER8> German here. I once drove an Audi A8 from Hanover to Berlin (while working for a car rental company). It was pretty much 250kph (155 mph) all the way (except where there was a speed limit of course). Definitely an insane experience. My hands were extremely sweaty. Yet I couldn't stop driving that fast. In that type of car, you don't really notice it anyway. But you DO notice it when suddenly another car is getting into your lane, seemingly far ahead, but within a few seconds you're so close that you have to hit the breaks really hard.

It's fun and all and a few years ago I would have hated that type of "paternalism" by Volvo. But now, with self-driving cars around the corner and my own more mature understanding of human fallibility, I would argue that it makes little sense that humans do drive at speeds higher than around what Volvo is aiming at.

<comment><USER9> You driven like that once, some people drive like that daily. Usually it's not them causing accidents. Whatever, anyone can be fast in a straight line.

<comment><USER10> > Usually it's not them causing accidents.

I hear that all the time, do you have a source?

<comment><USER9> In the current climate regarding the speed limit in Germany? Good luck. It's from experience, you know, seeing it from the perspective of the fast driver. I know it's another slogan but driving slower makes one more suspectible to distraction.

</comment></comment></comment></comment><comment><USER11> Just out of curiosity, am I the only one that's tried the top speed of every car I've owned? German cars have limiters at 130 or 155mph, and the first time I hit the 130 limiter was a surprise (suddenly lost acceleration, thought I had an engine problem, then realized I just hit the limiter).

Surely I'm not the only one? Intended out of real curiosity

<comment><USER12> Many places in the USA, passing a cop while hitting the limiter would result in at least a night in jail, instant driver's license loss, and lots and lots of money. The vast majority of Americans cannot afford even a basic speeding ticket, let alone that kind of expense. So no, you aren't the only one, but certainly experiencing that kind of risk is a massively luxurious thing that the vast majority of people cannot afford.

Also not everyone has access to long stretches of highway with little traffic to do this in a way that doesn't endanger other people

<comment><USER13> "experiencing that kind of risk is a massively luxurious thing that the vast majority of people cannot afford"

That seems a strange way to characterise breaking the law.

<comment><USER12> If you have enough money or resources there are plenty of laws you can afford to break.

<comment><USER13> You wouldn't say that Musk being fined $20 million by the SEC were luxurious though.

</comment></comment></comment></comment></comment><comment><USER14> Any enthusiast wishing to operate their vehicle closer to the engineering limits will most likely flash the ECU anyway (or simply not purchase the vehicle if you lock them out via DRM). On top of that, I drive a 2010 Hyundai Genesis Coupe (3.8L); the car can reach 140mph or 150mph rather easily, can be found for under $10k.

However, with most vehicles on the road, the tires are more susceptible to failure than the powertrain is to not delivering the speed. (i.e. my all- season, mid-grade tires are only rated to safely operate up to about 130mph). I would expect this from Volvo, and for the people who care it's more of a moot point.

</comment><comment><USER15> Is there any particular reasoning as to that value? If we assume major highway limits of 70 mph and add an excessive 20-30 mph for passing, that's still a ton of extra lethal kinetic energy.

edit: Apparently even the Autobahn has a recommended speed of 80 mph (I'm aware you can go faster, but then why have a limit at all?)

<comment><USER16> As I mentioned in another comment, tires with an "S" speed rating go to 112 MPH, while tires with an "H" rating go to 130 MPH. I'm guessing they either downgraded the factory tires or were concerned about lawsuits from owners who installed aftermarket "S" rated tires.

<comment><USER17> Lower speed rating also usually means lighter construction and a 'harder' compound, both of which reduce cost and improve fuel milage.

<comment><USER18> Actually it's the opposite I believe, at least for the same family of tires.

Sure there are high efficiency tires with harder compounds and are more efficient.

But if you get the sporty tire from whatever brand the higher speed ratings generally have the less flexible/harder material. The limiting factor being the heat generated from the flexing builds up. So generally a 150 mph rated tire gets less traction, costs more, and is worse when it's cold than a 112 mph rated tire.

So even on a fairly sporty car and tire you are best off getting the lowest rated tire that will accommodate your max speed.

<comment><USER17> Conceptually that may be true, but it's next to impossible to get performance tires in speed ratings under W and within any particular model it often varies only by 1, rarely 2, speed ratings.

</comment></comment></comment></comment></comment><comment><USER19> If I were automaker I'd consider allowing bursts above the maximum speed limit for a few seconds.

I'm not a fan of limiting (besides for warranty, electronics reasons) and prefer to educate rather than restrict. However, if taking this approach I believe you should consider that some people might drive in the limit and they deserve to be in power of their vehicles regardless.

Imagine if you drive near this software-limited speed and suddenly need to speed up a little bit more to avoid a dangerous situation. You simply can't. This may dangerous specially if you don't have in your mind that your speed is limited by software.

Just allow breaking out of this limit for, say, 5s so your drivers can get out of a dangerous situation instead... And if they try to abuse the system, disappoint them by blocking acceleration.

<comment><USER20> In all of my 32 years of driving and over many many miles I've had exactly _one_ situation where acceleration helped me avoid an accident and it wasn't anywhere near the local speed limit. On the way to visiting another HN user I was about to turn left and looking into the low sun waiting for a vehicle that was barely visible to pass. Then I moved across the lane and _another_ vehicle appeared quite close behind the previous one. Because of staring into the sun for too long waiting for the first one I had developed a really nice blind spot for the second car to hide in. It wasn't visible to me until it was almost on top of me. That's the only time that a large engine ever made a difference (and I'd never really floored it all the way in city traffic before but that was impressive). All the other times it was the brakes that saved the day.

<comment><USER19> Regarding sudden acceleration (and it's a good time to remember acceleration isn't speed) avoiding accidents...

I live in Brazil. There is a tax supposed to cause road accidents here. If your powertrain is > 1.0, the tax you pay when buying cars has a sudden increase. Therefore, many if not most people buy 1.0 cars here (). This is valid even for some that are not consider lower end here (though would be anywhere else in the civilized world).

It's actually the most common type of crash on highways here: [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3907522/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3907522/)

Anyways, one great reason of accidents here is frontal collisions. People either don't take into account that they are driving snails, not cars, and try to take over on the road but fail to do so at an adequate distance.

The thing is if you are at, say, 80km/h it gets really hard to increase your speed 5 or 10km/h in short amount of time. I believe that people driving powerful cars don't think about this often, and all it takes is an idiot to tailgate you while you are trying to take over to make shit happens. Another unfortunate thing is that you might find yourself tailgating the vehicle upfront before taking over it to reduce the needed distance.

* highways here are usually one lane each way most times. Sometimes two. I love when I go to southern California for work, and there are 12 lanes with almost no traffic (yes, traffic here is worse than there).

[https://www.fhwa.dot.gov/policyinformation/tables/01.pdf](https://www.fhwa.dot.gov/policyinformation/tables/01.pdf)

<comment><USER21> > If your powertrain is > 1.0, the tax you pay when buying cars has a sudden > increase.

What do you mean? Engine displacement>1L? Transmission overdrive? Something else?

<comment><USER19> Engine displacement > 1L (in fact, > 999cm³).

Not sure if these values are still valid, but if they are not they should be even worse nowadays.

Made in Brazil: < 1L: 30.6% 1L to 2L - 34.6 or 36.6% (gas + ethanol) > 2L - 41.6% or 48.6% (gas + ethanol)

Imports: < 1L: 60,6% 1L to 2L - 64,6% or 66,6% (gas + ethanol) > 2L - 71,6% or 78,6% (gas + ethanol)

Also, immediate availability is lower and most cars are manual with no cruise control :(

And obviously you'd already be paying a little bit more for a more powerful engine, so the increase is actually at least 10%, and most lower income people just get stuck with 1.0 for their whole lives...

[https://www.noticiasautomotivas.com.br/automovel-recolhe- de-...](https://www.noticiasautomotivas.com.br/automovel-recolhe- de-31-a-79-do-preco-em-impostos-no-brasil/)

</comment></comment></comment></comment></comment><comment><USER22> I see a lot of commentary on break quality and stopping distance.

Those things matter, but not as much as reflex response time, which is mostly a fixed constant for most people.

Going faster means you travel further before even getting to the brakes.

</comment><comment><USER23> We already have systems that can read speed signs. What I'd like to see is image recognition systems that recognize a school bus and when it is stopped.

Couple of times a year I see drivers blowing by a school bus as kids are getting off and trying to cross the street right in front of them. Be nice if the car decided for the driver that it was stopping.

</comment><comment><USER24> Off topic, but neat speedometer trick.

Preconditions:

* You have an analog speedometer which is in both miles and km/h. [1]

* You are on a road trip on a highway, driving at or near 100km/h.

In Canada on the 400 class highways, both are often true.[2]

The trick is simple. It must be, I figured it our when I was a kid looking of my father's shoulder while he drove.

Notice how 100km/h nearly aligns with 60 mph on the speedometer? You can use the mph gauge as the approximate number of minutes required to travel a given distance in km.

Say you just saw a sign saying a rest stop was in 42 km.

To estimate the time to your rest stop, just line up 42 km/h with the corresponding number on the mph scale, which in this case gives about 27 min.

[1] [http://www.storiesfromschoolaz.org/wp- content/uploads/2013/0...](http://www.storiesfromschoolaz.org/wp- content/uploads/2013/03/read-for-speed-0-to-120.jpg)

[2] I drive at 110 because the trucks drive at the same speed, so you don't have to pass as often.

</comment><comment><USER25> Bummer for track folks.

It's easy to get a new set of rubber that has a speed rating higher than what the factory provided; It's a lot more difficult for a layman to flash out a speed limit.

It's a shame that less and less companies are producing products that take into account that perhaps the potential buyer might actually know better.

<comment><USER26> In Japan, the Nissan GTR unlocks the speed limiter when it detects it at a race track: [https://gizmodo.com/nissan-gt-r-detects-when-car-is-on-a- rac...](https://gizmodo.com/nissan-gt-r-detects-when-car-is-on-a-race-track- disabl-337096)

</comment></comment><comment><USER27> I would love if all cars had a cruise speed mode where I could say, I want the top speed to be 60, and it never goes faster.

The difference here is that I would choose this speed, instead of it being set only by the manufacturer.

It is also OK if the car had both limits, a manufacturer max and a lower max speed configurable by the driver.

<comment><USER28> Isn't this what cruise control is? Or do you want this to be a hidden limit, say for one's kids' cars?

<comment><USER29> Cruise control won't hit the brakes if you are going downhill and exceed your set speed. I think he's looking for the latter. Setting it to 60 is probably too low though unless the OP only ever drives in the city. I'm hoping he's not one of those people who immediately shove their way over to the far left lane of the interstate and never move until they suddenly jump across three lanes of traffic at the last second to take their exit.

<comment><USER30> Recent cars I've owned with computer-controlled manual (or "manumatic") transmissions (Ford SelectShift/PowerShift, Hyundai Shiftronic, etc.) will change gears and do engine braking to keep it in the right speed. Even in my ancient Honda Accord, throttle control is usually enough to keep it within a few MPH of my chosen speed once going 60mph+ on most highways I tend to drive on.

</comment></comment></comment></comment><comment><USER31> I've always wondered why the government sets speed limits but then doesn't enforce them on manufacturers. You can solve 99% of speed "crime" by making it illegal to sell a car that can break the speed limit.

<comment><USER32> You've never had a track day...

This whole page is filled with "Doesn't apply to me, so go for it", which seems like a really bad rationale to apply to hundreds of millions of people, potentially.

<comment><USER33> I seriously doubt "hundreds of millions of people" regularly go for a lap in the Nordschleife.

<comment><USER34> Especially given the mechanical wear, motor racing (Even karting) is a rich man's game

<comment><USER35> You don't have to be rich to drive on a track. Champ Car (formerly Chump) is racing with very inexpensive vehicles. I did a track day with a sub US$5000 car that was still faster than many others. People take rental cars to track days for a total weekend cost of under $500. Drag racing costs next to nothing for a normal car.

</comment></comment></comment></comment></comment><comment><USER36> This made me wonder what the top speed of my current car is (a very modest Škoda Yeti) and it is 111mph :-)

</comment><comment><USER37> Although 180 km/h looks reasonable, I'm not convinced this kind of solutions is the way to go. Speed limiters are not new and were sold on the idea that are improving the efficiency of the engine, burning the fuel better. To do the same thing in regard to safety however, is a bit humiliating or at least patronizing. People already are required to jump through non-trivial hoops in order to legally get behind the driving wheel and all that is to make sure they fully understand the implications of driving a high speed vehicle and accept the implied responsibility. We already took care of setting the proper speed limits through road regulations on the society level, and we do further limit those speeds by choice on the individual level on each driving session. This artificial limitation from the automakers is more akin to fearmongering based marketing stunt, something not derived from rational discernment but from tackling one's lizard brain fears.

<comment><USER38> I don't think it's fearmongering, especially when you consider that children are allowed to drive (at least here in the US, and with minimal training). This isn't about being a nanny state or keeping folks from driving fast cars (I imagine there will always be cars you can take on the track), it's about keeping everyone on the roads safer. Not one single time in my highway driving life have I encountered a NEED to drive that fast in any traffic maneuver. People die in high speed crashes all the time, I don't think anything about this decision is fearmongering, it's about the health and safety of those around you.

<comment><USER39> Every decision that restricts people is justified with "it's about the health and safety of those around you". It's not a convincing argument when it's used for everything.

Volvo does it so they can use cheaper tires without being liable.

<comment><USER40> If it indeed increases the health and safety of those around you, why is this not a valid argument?

</comment></comment></comment></comment><comment><USER41> Pretty cool, by establishing a top speed standard they could run reliable crash tests for the absolute worst case that the car could experience. Looking forward to the future of "No matter how you drive this car, it won't kill you"

<comment><USER7> People die every day in car crashes at far slower speeds than that. There's no way to guarantee a car crash won't kill you, even at normal highway speeds.

<comment><USER42> Plus if speed was really THE main factor, highways would be terribly dangerous. Or they're usually the safest when it comes to accident statistics.

So speed is not the main issue but it's a nice tool when you're a politician or you want to communicate.

For the Autobahn, wiki says:

In 2014, autobahns carried 31% of motorized road traffic while accounting for 11% of Germany's traffic deaths. The autobahn fatality rate of 1.6 deaths per billion travel-kilometres compared favorably with the 4.6 rate on urban streets and 6.5 rate on rural roads.

</comment></comment></comment><comment><USER43> Even when I was on the Autobahn (in a Volvo S6 no less) my max speed was 108 mph, and most of the time I settled in at 100 mph. But there will definitely be some people pissed off at this, as I saw people clearly going closer to 120 on occasion.

<comment><USER44> I cleared 150 mph as a teen 'cause the speedometer went that high and part of being in a new car was seeing if you could actually pin the speedometer.

However, that was a very stupid choice, and I'm glad no one got hurt. Outside of a track there is no valid reason to go over 100 mph.

<comment><USER45> I did 150mph on the Autobahn last year on my motorbike on a straight stretch with three lanes. I thought I'd play it safe and stay in the outside lane in case someone from the inside lane decided to overtake another. Two cars undertook me, albeit very considerately, on the inside lane at considerably higher speeds. At that point I felt defeated and decided to take things a bit easier for the rest of my trip.

</comment></comment></comment><comment><USER46> This should be matched with a lowered purchase price, because they're almost certainly going to be equipping cheaper tires w/a correspondingly low speed rating.

<comment><USER29> This is Volvo we are talking about. They weren't equipping their station wagons with Pirelli tires.

</comment></comment><comment><USER47> A fine example of segmentation. Most Volvo customers don't buy Volvos because they're fast cars. They buy them because they are safe cars.

<comment><USER48> Well, there is their Polestar [0] performance division, which suggests there _is_ such a market...?

0\. [https://www.volvocars.com/uk/cars/new- models/s60/variants/po...](https://www.volvocars.com/uk/cars/new- models/s60/variants/polestar)

<comment><USER47> There are quite a few M's compared to regular BMWs. How many Polestars does Volvo sell compared to their regular models?

</comment></comment></comment><comment><USER49> So my current car tops out at 163MPH (not a Tesla). Being in the Bay Area (a large parking lot is how I would describe the freeways) the chance of every going that fast is zero. It is possible (no admission of guilt) that I may have hit 120MPH once or twice very late at night on the I280. That being said, this limit bugs my libertarian views. The issue is of course all the people in a car that can hit a stupid level of speed (100MPH+), that lack the correct breaks, tires, handling for that stupid level of speed. Drive down the 17. It is a wreakfest of people that drive too fast on winding road without understanding that just because your engine can push does not mean the rest of the important car parts function at that level. The engine tech level in the standard consumer car has hit a possible speed level without effort that is not matched by the other parts of the vehicle. Pair that with someone that thinks, well it can go that fast so it must be okay...

<comment><USER19> This limit shouldn't bug you at all. If it's voluntary (you buy the car without coercion), there is nothing wrong about it.

disclosure: I'm a hard-core libertarian myself.

</comment></comment><comment><USER50> Great. Now just make an automatic transmission that's not a pile of junk.

<comment><USER51> In a couple years there will be no need for transmissions anymore...

<comment><USER44> ...or steering wheels.

<comment><USER50> or people

</comment></comment></comment></comment><comment><USER52> Suddenly can't accelerate because of stupid speed limit -> Death.

Due to this fear, many a person (including myself) will simply never buy one such car.

<comment><USER53> If one is in a situation on a typical road where accelerating beyond 112MPH is going to cause death, I'm not completely sure that limiting to 112 is the real issue.

<comment><USER54> Being chased by a psychopathic Volvo driver springs to mind

</comment></comment></comment><comment><USER55> So many movies are going to don't make sense anymore but it's about time we are anyway going to come to a world where we need to find amusement in something else

</comment><comment><USER56> I was a Formula 1 test driver virtually, building the simulators and test drives. Limiting it to 112 would limit it to gear 1 of 6.

That's laughable. You could eliminate the gearbox at all then on better, extremely expensive cars.

</comment><comment><USER57> I don't want Volvo, or a computer, or a mechanical system to kill my family because it didn't account for an edge case.

Everyone here is talking about normal highway use, but, as everyone knows, not all situations are normal. Bad things happen.

My imagination is limited, but for example: Fires can spread quickly and surround you (e.g. a valley with one road out), a tsunami can happen with only a couple of minutes warning, some hospital trips can't wait for an ambulance, sometimes people try to kill you (jealous ex? opposing political group or religion in some countries, who knows what the future holds).

So, die in a fire I guess, it's for your own safety.

<comment><USER22> I find this argument rediculous.

We should not allow a huge negative behaviour every single day, just on the off chance that there's a possibility it would restrict us in a very unusual event.

Hundreds of people should die because maybe we can save a few?

Makes no sense.

<comment><USER57> How many auto fatalities are a result of people driving 150? Almost none, I'd wager. So then is my argument still ridiculous?

Freedom has value. Just because we can force some people to do some things more safely in some cases doesn't mean we should always do it. Otherwise, we can just outlaw cars entirely and force everyone to only go places where rails take them at government-approved speeds.

<comment><USER22> Fortunately, somebody has actually studied this and has found that yes, speed does matter:

"In Rheinland-Pfalz, a 130 km speed limit was also introduced on a 167km section of the A61 in 1991 and has been retained since then. This measure was combined with a ban on overtaking for heavy good vehicles. The impact of these two measures was a 30% reduction in fatal and severe injury accidents (comparing one year after and one year before their introduction – Rheinland- Pfalz Ministry of Transport)."

[https://etsc.eu/wp- content/uploads/Speed_Fact_Sheet_1.pdf](https://etsc.eu/wp- content/uploads/Speed_Fact_Sheet_1.pdf)

<comment><USER57> 1] I'm not opposed to speed limits, I'm opposed to the car enforcing them even when there is an exceptional case it's unaware of.

2] You can drive super dangerous without driving super fast

3] Almost no one drives super fast

4] The same pdf also says the death rate is exactly the same on roads without speed limits as those with speed limits... but I assume we're going to ignore that part and other contradictory studies to drive your point home?

i.e. 67% of roads have no permanent limit, 67% of deaths occur there...

And then you'll say "yes but that doesn't take into account the traffic volume on those stretches of road"

and I'll point to something else, and it'll get old, and you don't appear interested in considering other viewpoints anyway.</comment></comment></comment></comment></comment>


Show HN: An app to find sustainable alternatives, and companies worth supporting - <AUTHOR> https://apps.apple.com/app/boycott-that/id1515041024 <comment><AUTHOR> My wife and I researched and made an app to help you avoid companies that perform animal cruelty, and with sustainable switches for everyday items

</comment><comment><USER2> i don't care (as much) for the trends that are shown in the marketing. it'd be cool if i could enter my own criteria such as specific conglomerate names (like nestle) or create advanced filters.</comment>


How to Design, Build and Test Small Liquid-Fuel Rocket Engines (1967) - <AUTHOR> http://www.risacher.org/rocket/ <comment><USER3> This book is a great resource, and I would recommend it to to any amateur model rocketry fan.

I'm starting University in September as an adult student of Computer Science and I'm planning to start a model rocketry society with the goal of putting a 9ft tube above the Karman line and recovering it safely.

I'm still deciding on fuels, but I'm strongly considering a hypergolic combination of catalyzed pure hydrogen peroxide and kerosene (I've already been granted a recipient competent authority from the explosives department for the storage and transport of usable quantities these for the use in a model rocket).

The primary reason for hypergolic fuels is because it doesn't require a complex combustion chamber / ignition set up. You can mix them together at ambient pressure and temperature and they will spontaneously combust producing heat, steam and pressure. If you can safely handle the dangerous fuels it's a much easier route to a liquid fueled rocket engine.

One of the difficulties in the UK is going to be finding somewhere to launch from: we don't have large swathes of unowned, unmonitored land and the restrictions the CAA (rightfully) place on launching near cities means that it'll have to be out in the sticks somewhere. I'll probably have to convince a farmer to let us blow up a couple rockets on the back of a fallow field a few times before we get a successful launch off the ground.

I'm trying to plan as much as possible and get all the requisite licenses (I already have a CAA unmanned surveillance drone operator ID, as well as exemption from the need for a flyer ID because I have my flight competency certificates, and exemption from the 400ft amateur flight ceiling as long as I issue a NOTAM (notice to airmen) 1 week before any test flights, and I'm insured by the UK Rocketry Association) in the hopes that people will "take me seriously" when I found the society.

I'm also working behind the scenes to set up partnerships. I've been in contact with Starchaser Industries and a few other aerospace companies nearby to have them sponsor the program, show us around their rocketry factories and hopefully give us contacts at their company we can bounce ideas off to see if there's anything we've missed, or any hazards we are hugely mispredicting.

<comment><USER4> > _If you can safely handle the dangerous fuels it 's a much easier route to a > liquid fueled rocket engine._

This kind of glosses over the whole hypergolic fuels are necessarily poisonous toxins that boil your skin if you touch them. To react with each other so quickly, they basically have to react with just about everything else as well - including human saliva, the liquid on eyeballs, and the liquid in your lungs.

This (extremely 60s styled) video is full of useful information about how dangerous hypergols are: [https://www.youtube.com/watch?v=Zha9DyS- PPA](https://www.youtube.com/watch?v=Zha9DyS-PPA)

<comment><USER3> In general, I would agree with you.

If you're dealing with umsymettrical-dimethylhydrazine and dinitrogen tetroxide, you're going to be in a world of pain trying to produce them, handle them and get them close enough to use in an engine without being so close that the fumes spontaneously ignite. Not to mention that the dinitrogen tetroxide boils at ambient temperatures, etc, etc.

Obviously, I was glossing over the danger (not something I do in real life when handling dangerous fuels, but probably something I do when writing a short comment on Hacker News) and anyone seeking to work on Rocket Engines needs to ensure that they consult with subject matter exports before, during and after any construction or launch preparations begin.

... With that disclaimer out of the way, in the grand scheme of dangerous fuel and oxidisers combinations, Kerosene and Hydrogen Peroxide are _significantly_ safer to handle than traditionally used hypergolic mixtures:

\- They are both liquids at ambient pressures and temperatures (don't underestimate the value of not needing highly pressurised canisters - <USER2> 2000psi in many cases - and cryogenic equipment, that's all mass you don't need to lift and failure states you don't need to control for)

\- Storage and deployment of AVTUR (Aviation Turbine Fuels) is a well understood procedure with pre-certified canisters.

\- Hydrogen Peroxide at sub-90%, and especially at sub 70%, purities is reasonably safe to store and handle, especially if you store it in an inhibited state and you're willing to have a suboptimal hypergolic reaction in return for a safer handling procedure.

\- The pressures and temperatures created when reacting these two liquids together in a combustion chamber are extreme, but not so extreme as to be outside the remit of an amateur team.

This all doesn't mean that these are safe to handle - and failing to properly respect rocket fuel results in death for yourself and others - but it does mean that they're safer to handle.

In a perfect world I would manufacture solid state rocket propellants, but in addition to the negatives of not being throttle-able and being hard to early- terminate, manufacture of solid rocket motors is a criminal offence in the United Kingdom and getting an explosives certificate is a long, daunting task.

<comment><USER5> > in the grand scheme of dangerous fuel and oxidisers combinations, Kerosene > and Hydrogen Peroxide are significantly safer to handle than traditionally > used hypergolic mixtures:

Are they? AFAIU the propensity for HTP to exothermically decompose was the main reason why it was abandoned in favor of IRFNA/NTO. I mean, if you're switching to something as nasty as NTO or IRFNA for safety reasons, whatever you're switching from has to be pretty bad!

See also the Kursk submarine disaster.

> Hydrogen Peroxide at sub-90%, and especially at sub 70%, purities is > reasonably safe to store and handle, especially if you store it in an > inhibited state and you're willing to have a suboptimal hypergolic reaction > in return for a safer handling procedure.

IIRC in Clark's Ignition the opposite was mentioned, namely that higher concentrations have better resistance to decomposition, presumably due to lower amounts of impurities which can get the decomposition reaction started.

<comment><USER6> > Are they? AFAIU the propensity for HTP to exothermically decompose was the > main reason why it was abandoned in favor of IRFNA/NTO. I mean, if you're > switching to something as nasty as NTO or IRFNA for safety reasons, whatever > you're switching from has to be pretty bad!

I'm not sure the switch to IRFNA/NTO is for safety reasons. There is simplicity involved - you don't need catalyst with them. The components themselves are easier to get by and to store. They however have their own nasty properties regarding safety. Also historically nitric acid was initially used with turpentine, which is a hypergolic pair.

Here are some comments on safety.

[https://yarchive.net/space/rocket/fuels/peroxide.html](https://yarchive.net/space/rocket/fuels/peroxide.html)

<comment><USER5> > I'm not sure the switch to IRFNA/NTO is for safety reasons. There is > simplicity involved - you don't need catalyst with them.

Yeah, good point, that's certainly an advantage.

> Here are some comments on safety.

> > [https://yarchive.net/space/rocket/fuels/peroxide.html](https://yarchive.net/space/rocket/fuels/peroxide.html)

Coincidentally(?) those comments stop in the year 2000, when the Kursk put a dent in HTP enthusiasm. For a while at least.

Not that I have any good solution either. Seems all high performance liquid rocket fuels have some nasty downsides.

For small scale applications N2O + some light hydrocarbon like propane or ethane could be interesting. But that seems to be quite immature, so could be some showstoppers ahead in that path.

</comment></comment></comment></comment></comment></comment><comment><USER7> Perhaps worth noting that this is not the Rocket Lab launching small liquid fuel rockets today. This Rocketlab seems to have been a mail-order publisher mostly of NASA public domain stuff, with some original material and other authors. This book would seem to be their magnum opus and one of their more popular products.

They sold this book and Apollo photos and other things out of the back of hobby magazines in the 60s and 70s. China Lake is home to a Naval Air Station, a major R&D location for rockets and other flying things, so it's possible it was a side gig by some rocket scientists there, but that's just a wild guess.

<comment><USER8> There is a great book that covers the development of the Sidewinder missile at China Lake[0]. Really interesting discussion of the management/organization of the missile program and how it was so successful given it's small size and limited resources.

[0]: [https://www.amazon.com/Sidewinder-Creative-Missile- Developme...](https://www.amazon.com/Sidewinder-Creative-Missile-Development- China/dp/1591149819)

</comment></comment><comment><USER9> As someone who attempted to build a small liquid fueled rocket engine in high- school, this was one of the only texts I could find at the time that went into the subject in enough detail to be useful. (circa 2007)

<comment><USER10> See also: "Rocket Propulsion Elements", by George Sutton. Now in its 9th edition.

</comment></comment><comment><USER6> A great historic document. Today some better ways, in some aspects, could be proposed, but this is still a workable recipe.

<comment><USER8> Do you know of any more recent resources than this one?

<comment><USER10> The standard text on the matter is "Rocket Propulsion Elements", by George Sutton. Another recommended reference is "Design of Liquid Propellant Rocket Engines" by Dieter K.Huzel and David H.Huang.

</comment></comment></comment><comment><USER11> What depresses me is the section on "The Law". I did a lot of model rockets (just the regular solid fuel type) with my son. A fun educational hobby. There are very few place in Southern California where you can legally launch a rocket, even though they are extremely safe in comparison to the ones described here.

</comment><comment><USER12> Related (but sadly sold out) plans for a home rocket engine for your bicycle or go-kart: [http://unitednuclear.com/index.php?main_page=index&cPath=28_...](http://unitednuclear.com/index.php?main_page=index&cPath=28_47)

</comment><comment><USER13> Seems like a great resource for rocket engines.

Having a simulator to try these out would be very useful before trying anything practical. I'm sure it will be a complicated piece of code with heavy computation requirements

<comment><USER14> Simulation and validation is a touch improved, when I did this in college we used Ansys supplemented with data from NASA's CEA (Chemical Equilibrium and Applications) utility for validation. Once you get the work flow figured out it's not terrible.

Simulating cooling channels//ablation for larger scale rockets is a major PTA though.

</comment></comment><comment><USER15> This reminded me of the Popular Mechanic's encyclopedia set we had growing up. Basically an encyclopedia of DIY projects. Looking back it's something i definitely did not appreciate enough.

</comment><comment><USER16> Is it easy to procure liquid oxygen as an amateur builder? The guide looks like it recommends using gaseous oxygen and gasoline since it is readily available.

<comment><USER3> The typical way to produce small scale liquid oxygen (LOX) requires liquid nitrogen (you use the liquid nitrogen to cool the gas as it passes through some transport medium like a copper pipe and collect the cooled liquid).

Purchasing LOX isn't too difficult, there are many vendors willing to supply large amounts of it, and a few vendors willing to supply small (experimental) amounts of it.

Storing LOX is the real challenge, you need to keep it at ~310f (~-190c) which requires a well insulated cryogenic storage chamber. Typical industrial sized storage tanks have a few metres of insulation to keep the heat out, and typical small-scale tanks have around 1-2 feet of insulation.

You're probably looking at a viable minimum storage container size of between 500-1000 litres (any smaller and your insulation layer will be so thin that you'll lose 10-20% of your stored oxygen as gases per day), with the typical minimal size being in the 2,500 litres range (which normally lose 1-2% of stored oxygen to gas per day)

You can buy very small containers (2l, 5l, 25l, etc, these are for nitrogen but you can get them for oxygen too): [https://uk.vwr.com/store/product/2104367/liquid-nitrogen- dew...](https://uk.vwr.com/store/product/2104367/liquid-nitrogen-dewars-for- storage-and-transport-ld-series) but these lose the liquid _very_ quickly and you would likely want them delivered the same day you need them, resulting in a just-in-time delivery failure point.

</comment></comment><comment><USER17> Interesting material but shame it uses imperial units</comment>


Ask HN: What industries will be the most resistant to this crisis? - <AUTHOR> <comment><USER2> Utilities. Agriculture/food production (a subset of the sector often called "Consumer Staples").

However, that information isn't very useful now. The difference is already priced in.

</comment><comment><USER3> Funereal services. Food delivery. Residential utilities (until deep recession hits). TV (reruns at least). Gaming (in the short term).

</comment><comment><USER4> Any industry that produces basic human needs such as basic foods and living supplies.

</comment><comment><USER5> Bonafide needs, to the detriment of superfluous wants.</comment>


Ask HN: What do you use for BDD in Python? - <AUTHOR>

Python has several solutions for Behavior Driven Development such as Lettuce, Behave, Pytest-BDD, PyVows, Freshen, and probably others I haven't heard of yet.<p>What are you using, what are your testing with it, and what makes it better for that purpose than the alternatives? <comment><AUTHOR> Links to the Python BDD packages I am aware of, if you want to check them out:

* Lettuce: [http://lettuce.it/](http://lettuce.it/)

* Behave: [https://pythonhosted.org/behave/](https://pythonhosted.org/behave/)

* Pytest-BDD: [https://github.com/olegpidsadnyi/pytest-bdd](https://github.com/olegpidsadnyi/pytest-bdd)

* PyVows: [http://heynemann.github.io/pyvows/](http://heynemann.github.io/pyvows/)

* Freshen: [https://github.com/rlisagor/freshen](https://github.com/rlisagor/freshen)

</comment><comment><AUTHOR> A related post: [https://news.ycombinator.com/item?id=8373891](https://news.ycombinator.com/item?id=8373891)

</comment><comment><USER2> +1 Behave!

<comment><AUTHOR> So what are you using it to test, and what makes it better for that than the alternatives?</comment></comment>


Mathematics for Computer Science - <AUTHOR> http://courses.csail.mit.edu/6.042/spring12/mcsfull.pdf

<comment><USER3> This looks excellent. I also heartily recommend Knuth's _Concrete Mathematics_ ([http://www.amazon.com/Concrete-Mathematics-Foundation- Comput...](http://www.amazon.com/Concrete-Mathematics-Foundation-Computer- Science/dp/0201558025/ref=sr_1_1?ie=UTF8&qid=1332445763&sr=8-1))

<comment><USER4> This book has a great chapter on recurrence relations. Saved my ass in an algorithms course iirc.

</comment></comment><comment><USER5> I teach a number theory course to gifted high school students. I've been using these notes for two years now to plan lessons and find exercises. Great resource. You can also find more materials for the same course on MIT OpenCourseWare.

</comment><comment><USER6> Just a question for CS graduates here, how many Math courses were required to major in CS?

When I was an undergraduate the bare minimum was:

\- 2 algebra (number theory + linear algebra)

\- 2 calculus (single variable)

\- 2 statistics

\- 1 logic

\- 1 combinatorics (graph theory + enumeration)

There was no "Math for CS" course per say, there was just math you should know. And that was the bare minimum for a BCS, the BMath (CS) had even more. I myself struggled with those courses (mostly the "raw" math courses rather the CS-y ones) but I'm grateful now that I did them. Math and Computer Science are so intrinsically linked.

<comment><USER7> At Carnegie Mellon, the following are required:

      * elementary discrete math
      * intermediate discrete math / intro CS theory
      * calculus I
      * calculus II
      * linear algebra
      * probability
      * an "algorithms and complexity" elective:
        combinatorics, graph theory, automata, etc.

I might be missing one or two.

<comment><USER8> This is assuming you don't count the algorithm design and analysis class as math, or any of the "logic and languages" (Intro PL, constructive logic, Automated program verification, basic logic, computability and incompleteness) as math.

</comment></comment></comment><comment><USER8> I find it somewhat strange that generating functions are introduced significantly before recurrences are (and that recurrences are introduced last!). Does anyone know why the authors did that?

<comment><USER7> Recurrences are partially covered in chapters:

      13 (Sums and Asymptotics)
      15 (Generating Functions, as you mentioned)
      19 (Random Processes)
      20 (Recurrences)

and though they're not explicitly named as such in Chapter 5 (Induction), several of the problems in the chapter make use of them.

It seems to me that the first half of the chapter on recurrences covers recurrences more from a CS viewpoint such as the recurrence they list for mergesort:

      T(n) = 2 T(n/2) + n - <USER2>

which is arguably less fundamental than the study of linear recurrences which come up more often in math. The second half of the chapter covers techniques for solving general recurrences, both for general linear recurrences and general divide-and-conquer recurrences using the Akra-Bazzi theorem (which is an extension of the Master Theorem).

Thus, perhaps the chapter "Recurrences" is misnamed – the authors certainly cover elementary recurrences in the earlier chapters and leave more complex topics recurrences (such as how to solve them in general) for the end because they are less important than most of the other topics in the book.

</comment></comment><comment><USER9> Great to see it completed. The previous draft was salvation for my graph theory course. I think Mathematics for Computer Science offers very good understanding without unnecessary jargon or formalisms that obscure more than they clarify. Truly excellent introduction. In the same spirit I'd like to recommend the books of Walter Warwick Sawyer, and the "How to Ace..." books of Adams/Hass/Thompson.

</comment><comment><USER10> I took this class (6.042) as a sophomore a few semesters ago. I wasn't terribly good at it. Additionally, the professor and staff were a real pain in the ass, so I didn't really have the best experience. I remember they were writing this text my year. They made us do reading assignments critiquing each section. They were basically having us proofread it for them.

<comment><USER11> I think this is somewhat standard practice in classes where the prof is writing a book. I think I've done it a couple of times, at least. (By the way, you should've taken it F10!)

<comment><USER10> >"By the way, you should've taken it F10!"

My god, yes. I wish I would have had the foresight to have done it earlier rather than in the Spring. I am definitely not a fan of TEAL.

</comment></comment></comment><comment><USER12> I really like this book, it start with the very basics: Discrete Mathematics with Applications ([http://www.amazon.com/gp/product/0495391328/ref=oh_o04_s00_i...](http://www.amazon.com/gp/product/0495391328/ref=oh_o04_s00_i00_details))

</comment><comment><USER13> I took this class last semester!

As a mechanical engineering major who is interesting in computer science I really enjoyed it (the Psets were a bit annoying sometimes though). The text is pretty easy to read too.

<comment><USER10> Was it TEAL last semester? That's really what made me dislike the class the most, as well as the less-than-helpful staff.</comment></comment>


Tupac image performs at Coachella [video] - <AUTHOR> http://thenextweb.com/shareables/2012/04/16/amazing-video-technology-brings-tupac-back-to-life-at-coachella/ <comment><USER3> The technology behind this is <http://en.wikipedia.org/wiki/Musion_Eyeliner> which uses the old Pepper's Ghost trick: <http://en.wikipedia.org/wiki/Peppers_ghost>

<comment><USER4> This led me on a one-hour Wikipedia detour and I now possess detailed development knowledge of Disney's Haunted Mansion theme park ride.

Seriously cool stuff.

<comment><USER3> There's only 37 minutes between my post and your reply :-)

<comment><USER5> "I now possess detailed development knowledge of Disney's Haunted Mansion theme park ride"

Bending time included.

</comment></comment></comment></comment><comment><USER6> A bit more info - the tech behind this is a 2d variation on the Pepper's Ghost illusion ( <http://en.wikipedia.org/wiki/Pepper%27s_ghost> ), apparently licensed from Musion (<http://www.musion.co.uk/>). It's had previous outings - animators at Square Zero have used it several times, including to recreate Frank Sinatra. <http://www.squarezero.co.uk/what-we-do/holograms>

It's interesting to see their videos from 2010, which are still quite realistic but look stilted compared to the Tupac projection.

And obviously these aren't really holograms. I'm not connected to this in any way, just looked it up earlier since none of the articles mentioned what was driving this.

</comment><comment><USER7> Coachella has done a lot of innovative tricks this year. I was impressed that anyone in US could watch three of the stages live on YouTube. Live concert footage and other live videos on the web are going to quickly make TV feel overpriced.

<comment><USER8> even more impressive that I could watch it from Austria - by now so much content is region-restricted that this was a pleasant surprise.

<comment><USER9> Agree so much from New Zealand, me and heaps of my friends were all massive fans of At the Drive In when they were around, being able to see them live on the other side of the world felt pretty cool.

</comment></comment></comment><comment><USER10> I wonder if Jobs will introduce a new Apple product in 20 years.

</comment><comment><USER11> Love the technology, but is anybody else just a _little bit_ creeped out by this?

<comment><USER3> I'm less creeped out by the technology than by the implications in terms of copyright. What this may mean is that a copyright holder on the image of a person (such as Tupac) will be able to milk that image long after they are dead and potentially without having to pay anyone.

When you see Snoop Dogg 'performing' with Tupac you have to wonder where the money is flowing. Tupac's gone, perhaps his family is getting some pay back from the fact that an old recording of a song is played publicly. But what happens when Tupac suddenly records a new song? Would not surprise me to discover that the record companies are able to claim that they deserve all the money associated with that.

<comment><USER12> It makes me wonder how Snoop must feel, having performed that same song many times with Pac before...

<comment><USER13> Probably made him feel rich.

</comment></comment></comment></comment><comment><USER14> I'm confused as to how they got him to say "Coachella". Had he performed there in his lifetime or did they have to create that word from old voice recordings?

<comment><USER15> I'm pretty sure with enough voice data you can make people say just about anything, and Tupac left behind a ton of voice data.

<comment><USER16> Yep. See the work of cassetteboy: <http://www.youtube.com/watch?v=_m2pFYYEiko> (NSFW language)

All they use is soundforge, and it's trivial. You can achieve perfect results with modern software and algorithmic assistance.

<comment><USER17> Wouldn't it be easier to just hire a voice actor or impersonator?

<comment><USER18> They did use a voice impersonator.

<comment><USER19> source?

</comment></comment></comment></comment></comment></comment><comment><USER20> Here are details on how they reproduced Sinatra, which is probably similar to how they reproduced Tupac:

[http://www.damonchernavsky.com/News_Archive/October_2009/Hol...](http://www.damonchernavsky.com/News_Archive/October_2009/Hologram_of_Frank_Sinatra/hologram_of_frank_sinatra.html)

</comment><comment><USER21> Now we just wait for someone announcing his own version of Tupac made with HTML5 & WebGL.

</comment><comment><USER22> William Gibson - <USER2>

<http://www.amazon.com/Idoru-William-Gibson/dp/0425190455>

</comment><comment><USER23> Was that video image mixed&cut from the videos of his previous performances? Or was it computer generated?

</comment><comment><USER24> the [video]: <http://www.youtube.com/watch?v=ULrFtjaixbY>

</comment><comment><USER25> Great question that was asked today was, "would you pay to see a dead artist perform in holographic form"?

Think about all the artists you could bring back and have perform for people when using this technology.

<comment><USER26> Yes.

Honestly, I'm not at a show to watch somebody perform their music, I'm there to enjoy that music with a few hundred/thousand other people, and listen to it on a big stereo.

It's a socializing thing, not a consumption thing.

<comment><USER25> I think most people are in the same boat with you. When you are young you tend to push close up to the stage or jump into the thick of things, maybe because you like mosh pits.

When you get older it's all about going to hear how well the band performs live and enjoy a tasty adult beverage. Most entertainment venues I visit now I end up standing toward the back.

</comment></comment></comment><comment><USER27> Anyone know what kind of technology they used to do this? I haven't been able to track information about it down.

<comment><USER28> Probably Musion Eyeliner:

<http://en.wikipedia.org/wiki/Musion_Eyeliner>

<comment><USER29> Very impressive technology! I just wish there was a better name for it.

Any suggestions?

</comment></comment></comment><comment><USER30> so what's the law on profitting off someone's avatar like this?

<comment><USER31> Was wondering that too; only thing I found was this: [http://www.vh1.com/music/tuner/2012-04-17/whos-getting- paid-...](http://www.vh1.com/music/tuner/2012-04-17/whos-getting-paid-from- tupacs-hologram-resurrection/)

It says Dre got Afeni's blessing and made a contribution to Tupac's foundation for his image rights, but I now wonder if this gives him and Aftermath Entertainment unrestricted rights to capitalize off Tupac's hologram in all future concerts.

</comment></comment><comment><USER32> So after this is perfected, you could grab my image, make it look like I was the person who held up a bank and shot a hostage, and all the eyewitnesses would say it was me, and could give a positive ID? What would hidden security cameras show?

<comment><USER33> They would probably show a crew of tens of people installing a mirror system, cameras, sound, etc etc in the bank, and then a half-translucent image of you (maybe) coming in and awkwardly robbing it, if the tellers were in on it and had rehearsed beforehand so the recording of you could look in sync with their actions. Also, they couldn't hand you any objects.

It'd be easier for someone with a balaclava to rob the bank and plant the money in your house before an "anonymous tip", really.

<comment><USER32> That is today's version. 20 years ago the equivalent of an iPad 3 was $400,000 dollars and consumed 3 kilowatts continuously.

</comment></comment></comment><comment><USER34> Great effect but how did they get the footage of pac so clean? is it a 3d model?

<comment><USER35> My understanding is that the team at Digital Domain (pirates of the caribbean, Jeff Bridges in Tron) modeled the body, and then used mo-cap on an actor who did the "performance".

</comment></comment><comment><USER36> Tupac not Tupcac!

</comment><comment><USER37> [http://www.youtube.com/watch?v=sJ5hK-D8kRQ&feature=relat...](http://www.youtube.com/watch?v=sJ5hK-D8kRQ&feature=related)

</comment><comment><USER38> <http://cl.ly/3P3M3p3l1w002n220o1i>

</comment><comment><USER39> unreal. Not everyone might like Pac but amazing how real it looks.

</comment><comment><USER40> This should be titled "The Rapping Dead"

</comment><comment><USER41> somebody should get linus to perform live. I will buy the tickets.

</comment><comment><USER42> Next step: use it on someone good, like John Lennon or Jimi Hendrix

<comment><USER43> Just because you don't like rap doesn't mean your snark is wanted.

<comment><USER44> B.I.G. would have been a better choice.

<comment><USER45> I disagree. Musical preferences aside, this took place during a performance by Snoop Dogg and Dr. Dre and given their history and the Southern California location of Coachella, Tupac was the right choice. Not sure that either Snoop or Dre ever collaborated with B.I.G.</comment></comment></comment></comment>


A-2 System: The first open source project - <AUTHOR> http://en.wikipedia.org/wiki/A-2_(programming_language) <comment><USER2> Technically, in the days when programs were written directly in machine code, weren't they all "open source"?

</comment><comment><AUTHOR> At least according to Douglas Crockford (minute ~45 on <http://www.infoq.com/presentations/Heretical-Open-Source>)

<comment><USER3> I really wish people would put transcripts up for these video links. I can skim faster to the actual point than they can talk their way there.</comment></comment>


Contact Tracing with an ESP32 - <AUTHOR> https://github.com/tbensky/npct <comment><USER2> I have a similar project, but want to implement the full Exposure notification API. Maybe we can complement. [https://github.com/Lurkars/esp- ena](https://github.com/Lurkars/esp-ena)</comment>


Ask HN: As a developer, how can I learn to build investors presentation? - <AUTHOR>

<comment><USER2> Find a mentor who's done it, and learn from them. You can't beat experience.

<comment><USER3> Spot on. Techies think presentations are about transmitting information. They aren't. They are performances. Why do you think we call them "dog and pony shows"?

To learn how to put up a great performance, you either spend years gauging the response of your audience to discover what works, or you learn from a master.</comment></comment>


Are "landscrapers" the new skyscrapers? - <AUTHOR> https://work.qz.com/1146117/googles-new-london-headquarters-are-landscrapers-the-new-skyscrapers/ <comment><USER2> I think this is a silly use of real estate. The entire point of building an n-story building is you get to multiply your usable land area by n. Those who point to tall down-towns are right. A built up city has more land area than the map would suggest and can thus fit more people and more activity. Even better is the fact that a single utility link (electric, gas, sewage) to an n-floor building does the same work as n links to n 1-floor buildings. Its just more efficient.

I get the complaints about having to travel by elevator all the time and not having as much ground level community. Which is why I don't understand why sky-ways never became popular. There's no technological reason you couldn't have an interconnected upper level with shops and public/commercial space. Perhaps its just a problem on getting all the different developers and governments to agree on the standards for a modular interconnected second level.

<comment><USER3> One of the problems with tall buildings, especially super-tall ones, is the amount of interior that gets eaten up by non-usable infrastructure and support. For example, the Burj Khalifa in Dubai occupies about 17 acres (just under 7 hectares), while offering about 3.6 million square feet of interior floor space (about 83 acres or about 33.5 hectares) for a ratio of space:footprint that's < 5.

This means that if they simply occupied all the land and went up for 5 floors they'd have more floor space.

Example, the Pentagon in the U.S., with 5 floors and 6.5 million square feet has more usable square footage than the Burj, the tallest building in the world.

<comment><USER4> Burj Khalifa is not a utilitarian building, and clearly an outlier, so I don't really see why you would use it as an example except to mislead people. The Empire State Building which was mentioned in the article has 2.7 million square feet of office space built on 80k square feet of land.

<comment><USER3> It's an optimization problem. As buildings get taller and taller more and more of the interior space gets taken up by support framework, transportation and utility service bits. The Burj Khalifa is notable because it's also a case where in order to construct a building of its height, the _shape_ of the supporting infrastructure of the building is also fundamentally compromised such that there's less usable interior per unit height.

The Pentagon is interesting as a building because it was put up very quickly and remains one of the largest buildings by usable square footage in the world. But of course it's not a raw optimization. There's a 5+ acre center courtyard that's non-structural and each part of the pentagon is composed of 5 concentric "rings" with space between them for natural light to get into the building. Despite this, it's still a more efficient use of land acreage vs. the Burj.

</comment></comment></comment></comment><comment><USER5> No offense, but this is clearly a marketing fluff peice.

It looks like every other mid-rise commercial building development.

Is it the future? Absolutely, if by future, you mean the 80's, but everything is shiny and labeled with the adjective "smart" for some reason.

Almost as innovative as Apple's relabelling of the suburban office/business park.

When the hell did everything become marketing...

<comment><USER6> Yep, this is a Google overseas investment/tax dodge. Everything else about the building is secondary at best, for both Google and frankly, for the rest us too.

[https://www.theverge.com/2013/1/18/3889818/google- relocates-...](https://www.theverge.com/2013/1/18/3889818/google-relocates-uk- headquarters-to-kings-cross-london)

</comment></comment><comment><USER7> The only reason this is a "landscraper" and not a 50 story building is because of land use regulations, namely, London's height limits.

Asia, unburdened by the West's ridiculous land policies, is skyscraper heaven.

</comment><comment><USER8> Google's NYC building (111 8th Ave) is 790 ft long -- not as long as the new one's 1,082 ft, but still comparable. Few people realize it's NYC's fourth- largest building, since it's only 15 stories. [1]

[1] [https://en.wikipedia.org/wiki/111_Eighth_Avenue](https://en.wikipedia.org/wiki/111_Eighth_Avenue)

<comment><USER9> Google's 111 8th Ave NYC building completed in 1932, at 2.9 million square feet (270,000 m2), it is currently the city's fourth largest building in terms of floor area as of 2014. It was the largest building until 1963 when the 3.14-million-square-foot (292,000 m2) MetLife Building opened.

</comment></comment><comment><USER10> This doesn't seem a good idea. I don't think cities should sprawl even more. Even Silicon Valley would probably be better off if they had built up instead of all the one or two level office parks.

<comment><USER11> It would depend upon many factors. Height restrictions are one of them. There are social, environmental, and engineering considerations on that front. Current land use practices are another. It may be possible to gain tremendous boosts in density even with mid-rise buildings. Then there are the diminishing returns to land use while building up since you are talking about many independent structures that require a certain amount of separation.

These buildings are by no means sprawling office parks. They are simply the realization that horizontal may be better than vertical in some cases.

<comment><USER12> Monoliths are problematic. They're dull, they're poorly connected, they're in the way. It's worse when they're arranged horizontally because people tend to move horizontally. When you build up, the problems mostly develop for the people inside your building. When you build across, you obstruct everyone around you.

How are these "landscrapers" different from sprawling office parks? The key difference I notice is that the plan doesn't include an ocean of parking (which admittedly is a big part of why office parks are terrible).

</comment></comment></comment><comment><USER13> This is really no different than existing low story construction except connect the building instead of leaving them unconnected. If anything it's worse since there is now now variety at all, and enormous multiple blocks of sameness.

Part of what makes old-school cities so pedestrian friendly was having a variety of small shops to stop in. A bakery, grocer, butcher, clothing store all only a few windows wide. This is like building an enormous Home Depot, Costco and Circuit City in the middle of downtown. This does not make a pedestrian friendly city.

<comment><USER14> Doesn't a good portion of London (where this is built) already have whole blocks of low rise terraced housing? The only difference seems to be more holes in the wall and less doors.

</comment></comment><comment><USER15> "Landscrapers" will (obviously) have fewer, but larger floors. For certain types of organizations (e.g. software development organizations) this can be a real advantage, since more of the people that each person needs to work with can be on the same floor. Being separated by even a single floor can make a remarkably big difference to communication.

<comment><USER16> Interesting point. Reminds me of one of the major arguments in Jared Diamond's Guns, Germs, and Steels as to why the Old World conquered the New and not vice-versa.

Eurasia is a "landscraper" (oriented longitudinally) allowing for easier trade and exchange of innovations (especially related to agriculture and animal domestication) along a broad expanse of land.

The Americas are a skyscraper (more latitudinal orientation) with greater diversity of climate and topology that impeded the spread of some innovations and technologies.

<comment><USER17> Jared Diamond's thesis (rather like I feel the skyscraper/landscraper thesis is) is quite overstated. The climatic zones running from Mesopotamia to China are quite varied, and there's rather little evidence for technology transfer between these two endpoints. By contrast, the climatic zone from the northern edge of the Valley of Mexico to the boreal forests in Canada is basically one smooth temperature gradient, and we do know of rather extensive trading and tech transfer in North America (particularly, the introduction of maize to the independently-developed agriculture quite revolutionized developments in eastern North America). Not to mention the fact that the Americas don't seem so far behind Eurasia the more we do the archaeology: Norte Chico is now dated to at least 3200-3500 BC, a date competitive with Ancient Egypt and not too far behind Sumeria in terms of developing civilization.

</comment></comment></comment><comment><USER15> I was imagining a giant hole in the ground, but low, very long buildings are no doubt more practical.

</comment><comment><USER18> Why is it an era of landscapers when Google builds it but not even thought of when it is a regular shopping mall? Plenty of shopping malls with these sizes around the world. Also build as one long "landscraper". I would say landscapers are already there for many years, just not by a fancy company.

You build skyscrapers in locations where ground is scarce and expensive, you build landscapers in locations where it is the opposite. In dense areas with high ground prices you accept the building cost overhead, in other areas you go for cheaper building costs and accept the increased price on land (as compared to a skyscraper at the same location).

</comment><comment><USER19> I don't think the author is familiar with the Merchandise Mart in Chicago nor the Frank Gehry design of Facebook's new mega building (to cite 2 well known non US govt. examples).

</comment><comment><USER20> It's a "campus". That sure sounds cooler than "commercial office space".

</comment><comment><USER21> Reminds me of ibm's old boca raton campus (where they invented the PC and did OS/2 with MS). You could walk for a few hours down those corridors, it was just one long 3 or 4 story building, or at least that's how it felt.

</comment><comment><USER22> No, because skyscrapers are tall. They allow you to get a lot of working space out of relatively little of Earth's surface area. This thing doesn't offer anywhere near that sort of surface-area economy. They could get away with putting it in London, because London. Elongated buildings are commonplace in London, apparently because of local laws. If Google wants to build in a place where land surface area is precious -- downtown Manhattan, say, or any city in Japan -- it'll be hard to beat the good old skyscraper.

</comment><comment><USER23> I think the crucial technology which would make such cities practical in the future would be innovation in transportation, whether that be something like lateral elevators for short distances (of course "elevate" may be a misnomer here), or hyperloop for longer distances. Building vertically has the benefit of squeezing more utility out of land area, but has drawbacks which can make city life less comfortable.

</comment><comment><USER24> I love it. We do not live on Coruscant, space is not at such a premium even in London or NYC that you must push higher and higher. Skyscrapers are sterile; nothing happens at street level. The entire purpose is to isolate. The landscrapers have a more humane elevation and will end up creating entire neighborhoods.

</comment><comment><USER25> This style of architecture definitely allows for more sunlight and doesn't dirty the skyline with nasty highly reflective glass. Sometimes you're located in an area that is better without skyscrapers. Although I'm sure most of the posts here will be about "inefficiency".

</comment><comment><USER26> All the amenities made possible with high density but also convenient to take the stairs... Its a wonderful thing after living on the 33rd floor for many years. Interesting to see how this works out.

</comment><comment> King-Aaron > From some angles, it may resemble a landlocked cruise ship.

\- Does not look anything like a cruise landlocked cruise ship.

<comment><USER27> This, Sea World in Shenzhen, [1] is a mall built to look like a landlocked cruise ship. Google's building is not.

The U.S. Government used to build office buildings a few stories high but huge in length. The Pentagon is the most notable example, but there were many others built in the 1940s through the 1960s. They were built sturdily and cheaply, like parking garages.

[1] [https://youtu.be/NTcx0OHehdE?t=35](https://youtu.be/NTcx0OHehdE?t=35)

</comment></comment><comment><USER28> I wonder about the fire issues. I'd rather have two buildings with a gap to act as a fire break.

</comment><comment><USER29> It's just a normal looking building for that area, or am I missing something?

</comment><comment><USER30> Does this "landscraper" have the horizontal equivalent of an elevator (i.e. something where you push a button and it moves you anywhere horizontally in ~20 seconds)?

It seems like that might knock you over, but maybe there's a fun workaround (or just seats I guess).

<comment><USER31> From the article:

"Future employees might move around landscrapers on elevators that zoom back and forth laterally, not only up and down, she notes. That technology already exists in Germany, where ThyssenKrupp has recently sold the first elevator that can move up, down, sideways and diagonally—controlled by magnetic levitation—to a residential building in Berlin."

<comment><USER32> Why would you do something so bizarre when we have perfectly good conveyor belts, as used in most major airports?

<comment><USER14> Conveyor belts are slow. They realized long ago that you can't accelerate a standing human too fast and that stepping on to a conveyor belt takes you to max speed nearly instantly. Any faster and people need a running start to jump on.

<comment><USER33> Solved problem. There are actually moving sidewalks that accelerate you as they go, see [https://www.treehugger.com/urban-design/accel-moving- sidewal...](https://www.treehugger.com/urban-design/accel-moving-sidewalk- thyssenkrupp-dream-come-true.html)

Somewhere I saw a prototype of a multi-belt system as well. You get on a shorter one at normal speed, and you can either transition to one moving twice as fast as the first, or you can step off completely. The speed difference from stationary to slow is the same as from slow to fast - you just accelerate by shifting belts.

<comment><USER14> The link shows the "fast" speed as being 2m/s, which is still just a brisk walk. You'd be better off with bicycles or segways.

</comment></comment></comment></comment></comment></comment><comment><USER34> Strip malls, factories, and suburban office parks are all associated with dense, vibrant, walkable cities, so, yeah, this makes sense.

<comment><USER35> Please don't post unsubstantive comments here? I'm sure many of us share your sympathies. I probably do too, though it's hard to know for sure in the absence of any information. None of that matters, though, because this kind of comment just takes threads into internet brown.

We need better than this, especially early on, in order to have thoughtful conversation.

<comment><USER36> > Please don't post unsubstantive comments here?

I don't understand your question.</comment></comment></comment>


NASA to Explorers: Please don't touch our stuff - <AUTHOR> http://www.popsci.com/technology/article/2012-05/nasa-please-dont-touch-our-stuff-moon-travelers

<comment><AUTHOR> Of course I really hadn't thought about this, but if you do put a lunar mission together, and you can bring something back, and you bring back say the flag that Armstrong planted next to the Apollo 11 lander, just what would be the legality of that?

I always thought it would be cool to go see the site but a less scrupulous explorer might do like the British did to the Egyptians and just borrow those artifacts for their museum.</comment>


Ask HN: Why does Google say X million results and only gives up to Y? - <AUTHOR>

Why is it that Google will say 100,000,000 results but lets you only search up 1000. Also why is it that most of the results at the bottom are sometimes from the same site? <comment><USER2> I just did a search for "football checkers acequia moon" (without the quotes). It says there are about 11,400 pages, but when I go through them it ends up with 221 pages. I assume the estimation is based on some statistical predictions using the individual search words. Here they are relatively common terms (well, except 'acequia') which rarely go together.

I found <http://nielsenhayden.com/makinglight/archives/008851.html> say "I work for google these days, though not on search. The number of hits for phrases are estimates, based on overall word frequencies". The invalidity of the estimated results has been haphazard for a long time. See <http://danfingerman.com/dtm/archives/000004.html> from 2003.

</comment><comment><USER3> I imagine that the first part of the question has to do with paging. The first page is just the first n hits. But for subsequent pages they need to start at the beginning and skip page size * page number hits until they get to the hits for the current page. That gets expensive, so much so that they don't let you do it past 1000.

</comment><comment><USER4> Because they walk a small part of an index to figure out how many hits there _probably_ are.

Geez; you think they actually count a giant left join on the internet?

Also: <http://www.tbray.org/ongoing/When/200x/2004/11/26/SearchSort></comment>


An easier way to create GitHub repositories - <AUTHOR> https://github.com/blog/1105-an-easier-way-to-create-repositories <comment><USER2> Glad to see that I'm not the only one who doesn't know what to do with notifications on github.

<comment><USER3> Same here, my thought process whenever I see a new notification goes something like: "someone commented on my pull request? Two weeks ago? And I already replied to it?"

</comment></comment><comment><USER4> I read the headline and hoped that they had come up with a way to create new repos from the command line. That being said, this is a great improvement, especially with the templates.

<comment><USER5> Have you tried this? <http://defunkt.io/hub/>

        # create a repo for a new project
        $ git init
        $ git add . && git commit -m "It begins."
        $ git create -d "My new thing"
        → (creates a new project on GitHub with the name of current directory)
        $ git push -u origin master

<comment><USER6> I actually was trying to use hub as part of our workflow (pull request from feature branches) and it requires a user token that's no longer obtainable (that I could find) as github is deprecating it in favor of oauth. So I'm now building a cheap set of scripts using curl. If something has changed since this weekend, or if there is a fork or branch I missed that doesn't require the user token (or if you can get the token somehow), I'd love to know about it as hub fits all our needs perfectly.

EDIT: just checked on the issue and it looks like it had movement recently, so i'll be trying the possibly working branch.

<comment><USER7> > it requires a user token that's no longer obtainable (that I could find) as > github is deprecating it in favor of oauth.

Whoa, I had just used that feature last week. It used to be on the 'Account Settings' page near the password fields.

</comment></comment></comment></comment><comment><USER8> Sidenote motivated by "If you need to upgrade your account to add a private repository, you can now do that inside of the new repository screen." : You'd be really shocked how valuable paying attention to thirty seconds of the user experience can be when they're the thirty seconds separating an established software company from tens of thousands of credit cards.

</comment><comment><USER9> I guess I'm confused. Creating repositories was difficult?

<comment><USER10> I can't tell you how many times I spent > 5 minutes trying to find where to create a new repo for my organization.

<comment><USER11> Lucky you. I don't even know how to easily _see_ a list of my organizations. I always go through Account Settings -> Organizations.

That works but is rather counter-intuitive...

That said, I would have sworn sometimes there's a small dropdown next to my username with the organizations in it. But right now I can't reproduce it.

<comment><USER12> The problem is (probably) that you are watching github.com/yourprofile, which doesn't show the dropdown. When you go to github.com itself you will see the dropdown for selecting organisations in the top-left.

<comment><USER11> Yes, in the meantime I found it and have identified the underlying problem.

You land on three different pages for these links:

      A) The github logo (top left)

      B) My name in the organizations dropdown (when available)

      C) My name in the upper right

The solution is simple:

These 3 pages must be combined into one and the organizations-dropdown must be made visible on _all_ pages.

It's pretty obvious in hindsight, I can only assume the github frontenders are suffering from routine-blindness.

</comment></comment></comment></comment></comment><comment><USER13> Anyone else shocked about the 9000+ notifications unread? Isn't that admitting it useless?

<comment><USER14> GitHub really needs to allow users to control their notifications and activity feed with finer granularity.

There are projects I work on, which I want to appear in my activity feed. There are projects I want to bookmark, which I don't want in my activity feed.

Right now the signal:noise ratio is terrible for activity feed and notifications.

<comment><USER15> +1!

That's really important. Also if you e.g. receive a notification per email about something and go on this page by clicking the link it should remove the unread notification for this particular thing.

</comment></comment></comment><comment><USER16> Oh come on. Really, who cares about this?

Github has /so/ much more to fix before moving the New Repo button up to the top bar.

Cluttered news feed and activity stream and redundant notifications are issues that need desperate attention. Github, please fix them ASAP.

<comment><USER17> And we're working on /so/ much more than new repo screens too :)

<comment><USER18> For the love of all that's holy, please add issue sorting back, as requested hundreds of times on the blog post on that topic...

<comment><USER17> You can sort by Submitted/Updated/Comments. Feel free to send feedback to email@example.com if this isn't what you're thinking of.

<comment><USER19> masterleep is thinking of sorting by user prioritization. We miss it.

</comment></comment></comment></comment></comment><comment><USER20> Ha, the comments on that page look like an except from old school yahoo chat.

<comment><USER21> A/S/L?

</comment></comment><comment><USER22> I still want notification settings per organization membership.</comment>


Ask HN: Name of a Problem dependent on a problem dependent on a problem etc? - <AUTHOR> The software I have made that is now heavily used within the business has not scaled well with the growth of the company. Due to the customer timely demands, Instead, of re-valuating and re-factoring the source I made tweaks, workarounds, etc to meet the requirements.
Now when a new change is required, I have fallen into a scenario that goes something like this.
Management: We now need your software to do X Me: OK, this means I need to change the way Y works first, but this can't be done until the way Z is modifed, but this relies on A
Malcome in the middle expresses this beautifully: https://www.youtube.com/watch?v=AbSehcT19u0
When trying to explain this, I usually end up tongue tied and the end of the conversation usually ends up like
Management: We need yout software to do X Me: OK, give me a few days
Is there a general name describing this effect? <comment><USER2> Yes, the name of this effect is called Software Engineering.</comment>


Record and share terminal sessions – A lightweight, purely text-based approach - <AUTHOR> http://www.asciinema.org <comment><USER2> [https://news.ycombinator.com/item?id=9753537](https://news.ycombinator.com/item?id=9753537)

</comment><comment><USER3> I was using this for a while; until I discovered the 'script' and 'scriptreplay' commands that come with most unix systems.

You can start recording by running: `script -t timingfile typescript`. Your screen contents are recorded into the file `typescript` and the timing into `timingfile`.

You can play back by running: `scriptreplay -t timingfile typescript`

Check out the script man page for more cool things; like streaming live by using a fifo.

<comment><USER4> > You can start recording by running: `script -t timingfile typescript`. Your > screen contents are recorded into the file `typescript` and the timing into > `timingfile`.

Beware `-t` it's a non-standard (as much as script is considered a standard) extension:

* on OpenBSD there is no `-t` (or any other option aside from `-a` "append to existing typescript file")

* on FreeBSD and OSX `-t` specifies the flush time interval (in seconds, defaulting to 30) (on FreeBSD > 9.2 `-r` will save IO and timing data)

* on older linux distros it's a flag to output timing data to stderr

And scriptreplay is linux-only, NetBSD 2 and FreeBSD can replay sessions with `script -p`

</comment></comment><comment><USER5> This is really awesome. This is exactly what I've been looking for. Your service is compelling for me too as I've been thinking of doing some katas and putting them somewhere.

My only (very slight) quibble is that in perusing the terms of service you talk about having license to promote a user's profile/recordings. This is reasonable to me, but could potentially get in the way of moral rights if the profile/recordings are ever modified. So I don't mind if you modify my recordings, but I definitely mind if you modify them and then promote them as mine.

If there is any way you could modify the terms and conditions to indicate that you won't do that, then that would be great. In some countries (Canada for instance), it is not possible to waive your moral rights, so this is probably in your best interests too.

</comment><comment><USER6> Mind Blown! I watched the "video" and was like of this is great and the option to upload to a website not youtube made me go Meh. Then I read the following line.

> Oh, and you can copy-paste from here

You can copy and paste from the "video!" So when I give someone a tutorial on a command line tool they can copy and paste the codes themselves!

EDIT:

People can use the recording to show what they are doing to give them the error and display the output!

<comment><USER7> > upload to a website not youtube

I haven't dug into the details, but both the player[1] and the website[2] code are available so it should be possible to set up your own website if you like.

1\. [https://github.com/asciinema/asciinema- player](https://github.com/asciinema/asciinema-player) 2\. [https://github.com/asciinema/asciinema.org](https://github.com/asciinema/asciinema.org)

<comment><USER6> Well they are not videos and not able to upload onto a website without doing a screen recording. This tool actually is much better than making a video.

</comment></comment></comment><comment><USER8> I really like the use of login links and not passwords on their website. Is this becoming a trend?

</comment><comment><USER9> Thsi works pretty well:

[https://github.com/icholy/ttygif](https://github.com/icholy/ttygif)

Convert tty sessions to animated GIFs.

</comment><comment><USER10> This looks really cool! It's also the first thing like this I've seen which includes a nix installation section, double points!!</comment>


Alert: Your Plant Needs Water - <AUTHOR> http://online.wsj.com/article/SB10000872396390443921504577643460932560358.html

<comment><USER2> Twine is an interesting looking product, and 'connected everything' is most likely the future, but using tech to tell you to water your houseplants screams of engineering a problem to match a solution. (Which is, of course, the foundation of geek society.) Besides: I water my army of jades once a millineum (give or take a thousand years). If I go too long between waterings: no worries, they just grow roots above the soil and take water from the air.

Plants aside, I'm rather interested in where the 'connected universe' will take us. I'd much rather have my washer/dryer push a notification than buzz loudly or sit idle. Likewise with the snail-mail box once the postman's left a letter. And micro messages from my plants/oven/door mat shouldn't be hard on bandwidth; just a drop in the bucket compared to media delivery (video).

</comment><comment><AUTHOR> This to read the full thing: [http://www.google.com/url?sa=t&rct=j&q&esrc=s...](http://www.google.com/url?sa=t&rct=j&q&esrc=s&source=web&cd=1&cad=rja&ved=0CCUQqQIwAA&url=http%3A%2F%2Fonline.wsj.com%2Farticle%2FSB10000872396390443921504577643460932560358.html&ei=UOtOUILAFMasiQLzv4CQDQ&usg=AFQjCNF-2VABiNtbgxePM19kxQyYAqkJxA&sig2=UaEJ5tZP9dYx- ZQgsaEfLA)

</comment><comment><USER3> A hacker friendly gardening solution.

[http://makeprojects.com/Project/Garduino-Geek- Gardening/62/1...](http://makeprojects.com/Project/Garduino-Geek- Gardening/62/1#.UE-BehWMztZ)

</comment><comment><USER4> Hope the Twine ships eventually, it's such a slick solution. A few years ago I wired up my office basil plant to a moisture sensor so it could post to its Facebook page (Basil Green) when it needed watering. Being tethered to a computer was sort of overkill since the real data rate was three or four bits per day.

</comment><comment><USER5> Wondering: a device to monitor devices that can fail silently, good. But it needs two AAA batteries. When they discharge, does Twine fail silently? Do I need another Twine to monitor each Twine? Wait.. that can't work.

<comment><USER6> It can monitor itself. Emails when the batteries are running low.

</comment></comment><comment><USER7> Screw plants. Leave the washing machine alone. Just give me a WiFi-controlled wall switch and it will be a _huge_ step forward for everyone interested in home automation.

</comment><comment><USER8> Sounds like a distracting hell that I have somehow managed without.

</comment><comment><USER9> I wouldn't mind an autonomous squirt-gun that can distinguish between crows and cardinals, and can keep the former out of my bird feeder.

</comment><comment><USER10> I read this as "Alert: Your _Planet_ Needs Water"

</comment><comment><USER11> False: My cat ate my only plant.

<comment><USER12> You are new here. Just an alert: off topic silliness like this is not desired here. Reddit likes that kind of thing.

You have 1 karma at the moment. If your karma goes negative your account will be hell-banned, and you will not be notified when this happens.

<comment><USER11> Alright. Alright. Don't rustle your jimmies.</comment></comment></comment>


Getting started with Raspberry Pi and building a Google Photos digital frame - <AUTHOR> http://paulstamatiou.com/getting-started-raspberry-pi/ <comment><USER2> Pretty cool! Can you make a square version for my instagram photos?</comment>


We Know SUV Design Kills Pedestrians, but We Still Let Carmakers Sell Them - <AUTHOR> https://usa.streetsblog.org/2017/10/19/we-know-suv-design-kills-pedestrians-but-we-still-let-carmakers-sell-them/ <comment><USER2> Related: so called 'Bull Bars' are illegal in the EU, because of the damage they inflict on pedestrians even in light collisions: [https://en.m.wikipedia.org/wiki/Bullbar](https://en.m.wikipedia.org/wiki/Bullbar).

</comment><comment><USER3> We know yard design kills kids, but we still let landscapers sell them.

Having a yard that lets your kids play near traffic should be illegal because kids will run into the street. Why are fenceless yards still everywhere? Because those nasty homeowners want them.

The critical design factor is the low, non-existent fence, which allows people to go into the street instead of behind the fence.

Why are companies allowed to sell mass market yards with such a huge perimeter in front that children are able to cross? Where are the regulators at the National Yard Traffic Safety Administration?

</comment><comment><USER4> I've felt that SUV drivers should be required to pay much higher insurance premiums, as per a 'danger' factor.

You choose to drive a dangerous vehicle, you need to pay higher insurance for it.

On a similar note it's also annoying how there's no standard height for bumpers. Sometimes you see giant SUVs with bumpers at your head level (as an adult in a 'normal' car). In any collision the point of impact is right at your head. When I see those I question how that design could even be legal.

<comment><USER5> Either the actuaries have priced the increased risk into the premium or your fears are overblown.</comment></comment>


Ask HN: Are there reasons beyond efficiency for ART vs. Dalvik on Android - <AUTHOR>

Wondering if ART is designed to make it easier for Android to run on Intel architectures, or if there are legal reasons for the shift to ART. Understood that work on ART has been ongoing for a while and the previous principle architect of Dalvik left Google a while back. <comment><USER2> None that I've ever read (but I also don't work for Google, so external docs only).

ART improves app load times, runtime performance, and reduces battery usage. That effect is somewhat amplified by AOT-ing services/APIs that apps rely on, so instead of just seeing the improvements within a single APK, you might see a single app-load improved by three or more APKs being AOT-ed.

Not that dissimilar from Ngen in the .Net/CLI world.

Intel won't benefit more (or less) than other architectures. They're both doing the same work, just doing it at a different point in time. So unless Intel or someone has developed a really awesome static analysis tool which just happens to be too slow to shove into the JIT pipeline, it shouldn't make a huge amount of difference (and I've read nothing about an Intel specific dex2oat).

As to legal: Most of Google's issues with Oracle have been resolved. They related to a bunch of Oracle's patents and something about the Java library. ART doesn't really change how anything works, you're still interpreting bytecode into local instructions, you're still using the same libraries, and even the whole workflow hasn't really changed. Just moved around WHEN stuff happens not WHAT happens.

So while IANAL, I don't know if how ART would be a legal maneuver. If anything it exposes them to additional patent liability as the process is more complicated and third parties could claim they "own" part of it.

<comment><AUTHOR> Thanks, interesting commentary, and your point on Google / Oracle all makes sense.

One question regarding the architecture would be whether there is more of a performance improvement on x86 versus ARM for the ART pipeline compared to the pipeline for Dalvik.

ARM are saying Intel performance suffers mostly because of native code - [http://www.theregister.co.uk/Print/2014/05/02/arm_test_resul...](http://www.theregister.co.uk/Print/2014/05/02/arm_test_results_attack_intel/) while not speaking to performance of Dalvik versus ART on the two platforms. Intel are pushing their performance and scale while skipping over the native code question: [http://www.extremetech.com/computing/130552-intel- dismisses-...](http://www.extremetech.com/computing/130552-intel- dismisses-x86-tax-sees-no-future-for-arm-or-any-of-its-competitors) .

It sounds from what you say that ART doesn't really change the balance between Intel and ARM in any significant way, so that leaves the question of whether the problems Intel has with translating apps with native code compiled to ARM targets can be overcome by any manufacturing advantages Intel may enjoy.

</comment></comment><comment><USER3> ART is considered to be Dalvik 2.0. The main reason is that many of the choices made by Dalvik are no longer relevant in the current technical environment. SOCs have evolved a lot since Android 1.0 .

I doubt that ARM vs Intel has a lot of weight from Google's point of view.. it is not really Google's issue.

We can also hypothesize that ART more pluggable architecture is here to allow Google to maybe switch languages at some point in the future. There is nothing official in that regard though, quite the contrary (cf the I/O fireside chat where the Android team clearly said that Java is Android's language). So, either they are working on a replacement language in secret or this is just a nice result of the new build system and runtime.</comment>