Wikipedia:Reference desk/Archives/Science/2012 November 21

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November 21

Automated mini boats

Currently in the Gaza Strip, which is subject to a sea blockade, but also in many far-flung archipegaloes where the labor of hiring a person to make the ship may outweigh the tiny amount of cargo needed for a few residents, I would think that there would be an economic incentive for tiny ships that use GPS to carry cargoes to predetermined rendezvous points.

Now, it does occur to me that a scale model ship with a scale model boiler and a scale model screw probably ought to make only a proportionally reduced distance in a given amount of time, with fuel tanks proportional to its mass, and that therefore it should not be economical, or even possible to carry the fuel; ships are huge for a reason.

Nonetheless, model yachting using the wind exists, and the wind is, if anything, more powerful in regard to the scale vessel.

Is it possible that well-designed but very inexpensive automated model yachts could be mass produced to carry the food and medicine Gazans need past any blockade? (at least, until the Israelis have similarly tiny drone ships to attack them...) Wnt (talk) 00:15, 21 November 2012 (UTC)

Technologically speaking it's definitely possible, unmanned boats have successfully crossed the pacific[1][2]. However Palestinians may or may not have the financial or industrial power to maintain such a fleet. A8875 (talk) 01:22, 21 November 2012 (UTC)

I could see the Israelis building tiny unmanned gunboats to sink those teeny ships. Or better yet little galleys ("Ramming speed!").Clarityfiend (talk) 02:46, 21 November 2012 (UTC)

I see we have an article Liquid Robotics about these. From the site they crossed 3200 miles in 4 months, or just over 1 mph, which should be fast enough by the Lilliputian scales of the Israeli conflict. Unfortunately the site doesn't give any clear indication of the cost or even the payload of these things, so I'm still not sure how practical the idea is. Wnt (talk) 03:39, 21 November 2012 (UTC)

That would be a massive improvement to playing chess with real civilians.-- OBSIDIAN†SOUL 16:06, 22 November 2012 (UTC)

could probably be remote controlled via a satphone or such, assuming cell service doesn't reach out to sea that far.

this brings up one of my favorite hobbyhorses; military conflict today (as in the herein mentioned conflict) is awfully destructive and deadly, to civilians as well as combatants. yet, people seem to want it anyway. I suggest instead we go back to WWI era naval battles, with huge dreadnaughts blasting away at each other far enough offshore to be safe, but close enough for spectators. could even be a profitable entertainment. the catch being, they are unmanned, and operated by remote control. fills in that niche between football (soccer) hooliganism and thermonuclear destruction that we as a species seem to so dearly crave. Gzuckier (talk) 18:33, 21 November 2012 (UTC)

See Naval Warfare at Peasholm Park, Scarborough. Alansplodge (talk) 19:16, 21 November 2012 (UTC)

Why gunboats? RC helicopters could do the trick - just add an Uzi.

OS: +1. Gzuckier: "And in the Finals: Royal Oaks vs. Man U-boats, rofl. - ¡Ouch! (^{hurt me} / _{more pain}) 11:27, 23 November 2012 (UTC)

Pork v Chicken

Which would be more dangerous to do? Eat raw chicken or to eat raw pork? My friend claims eating raw chicken would be worse, but I would have guessed pork would be more dangerous. Which would be more likely to kill you or cause very serious illness? Rabuve (talk) 09:14, 21 November 2012 (UTC)

The only health risk mentioned in our Chicken (food) article is salmonella, which is normally not fatal in healthy adults. Undercooked pork, on the other hand, is known to carry Trichinosis, tapeworm and other nasties in addition to Salmonella. Rojomoke (talk) 11:24, 21 November 2012 (UTC)

The USDA maintains a website, Is It Done Yet?.gov, with the intent to inform the public about healthy and safe handling of meat and poultry. Neither pork nor chicken are safe to eat raw. Outside the realm of normal, safe, and healthy food preparation, if we wanted to answer your question, we'd need a clearer definition of "danger" and a method to compare different levels of danger. Statistically, more pork in your average grocery store has an infection of some type. According to the NIH and the USDA, in 1943, one in six Americans was infested with trichina worm as a result of uncooked or undercooked pork (trichinae fact sheet from USDA). So, from that perspective, though the statistic is grossly out of date, it's also grossly factual evidence that more pigs have worms, by the numbers, than percentage of chickens carrying contagious Salmonella bacteria. And yet, an argument can be made in either direction: salmonella is either more- or less- dangerous, if you get it, than trichinosis - even though different sources claim that you're more- or less- likely to contract it. Welcome to the world of quantitatively analyizing difficult and ambiguous data! So, is a more dangerous disease that is less likely to occur more or less dangerous? Nimur (talk) 14:18, 21 November 2012 (UTC)

The age of those stats is a huge caveat; the pork industry is much more regulated than it was 70 years ago. Due in part to pork's bad name, the industry made a huge effort to clean up the image and quality of the meat (cf. "The Other White Meat") to the point where guys like Alton Brown advocate cooking pork chops to medium rare - something that would be unheard of back in the 40s and 50s (I still can't get my elderly mom to cook them to less than "briquette"). I'd much sooner down a piece of undercooked pork than chicken, though obviously different pieces have different risk factors. Matt Deres (talk) 15:42, 21 November 2012 (UTC)

Every Tuesday I eat Mett and this is a very common here. So with proper veterinary oversight over the production raw pork does not cause any harm. It is common for decades and there is no significant illnesses or death atributed to raw pork consumption here in Germany.--Stone (talk) 20:51, 21 November 2012 (UTC)

The article suggests trichinosis is also very rare in the U.S. (11 cases) and usually not from commercial pork; nonetheless it also says "The CDC reports 0.013% of U.S. swine is infected with Trichinella," which I would think would suggest it isn't truly totally safe either. Wnt (talk) 10:38, 22 November 2012 (UTC)

I liked the chicken sashimi I had in Kagoshima and of course all those Mettbrötchen. No problems so far either. bamse (talk) 23:25, 21 November 2012 (UTC)

• Not every disease has been discovered, and limited awareness of recently-discovered diseases can hinder efforts to prevent them. For example, the prevalence of antibodies to (i.e. evidence of past infection with) Hepatitis E virus are quite high in Germany, but not high in Germans who avoid pork products (i.e. Muslims). The medical consensus is that eating undercooked meat is risky behavior when it comes to infectious diseases. Who knows what else is lurking out there? -- Scray (talk) 02:03, 22 November 2012 (UTC)

On the question of regional / cultural differences, you might look at Toxoplasma gondii#Human epidemiology. There used to be a line about the dramatic differences between France and say Britain, but I don't see that line in there now... but nevertheless, there are likely large differences between food preparation cultures that result in measurable differences in humans. Shadowjams (talk) 19:23, 22 November 2012 (UTC)

Why don't they just test if cellphones actually do cause interferences in airplanes?

Yes I have read mobile phones on aircraft and I have watched that old MythBusters episode, but why can't the FAA just test if cellphones actually do interfere with communication signals? According to the article, one theory is that the lack of testing is for cost reasons, and that to save money, it should be airlines doing the experiments. But are such tests really expensive? And why can't they just tweak the communication tools of the aircraft in such a way that cellphones can't interfere with the signals? Narutolovehinata5 ^tccsdnew 11:26, 21 November 2012 (UTC)

As I understand it, the main reason they don't let you use your phone on the plane has nothing to do with safety; it's because the telecoms don't like it. It confuses their equipment to have you moving so quickly from one cell to another. But I don't have a ref. --Trovatore (talk) 11:32, 21 November 2012 (UTC)

Another safety factor is the potential for assault and battery by other, irritated passengers who would have to listen to it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:29, 21 November 2012 (UTC)

The general issue has been discussed many, many times before on the RD, you likely want to read these discussions. However generally speaking, and our article reflects this, article communications systems are designed to be very robust and resist all sorts of interference. It is however difficult to completely prevent any possibility of interference and the small possibility of interference is one reason why there is general reluctance to allow such equipment, as both airlines and regulators tend to be very risk adverse. As I said, it's only one reason arguably only a small one, there are plenty of other reasons for any bans. Note that with the recent development of picocells on planes, airlines are started to get interested in deploying these and testing their usage together with phones sufficiently to satisfy regulators. This shouldn't be surprising, there's little incentive for airlines to pay for testing mobile phone network usage on planes when they generally won't work very well anyway when still trying to communicate with ground based equipment given the speeds involved and so the actual interest and advantage to their customers (passengers) is unclear and may be even a negative (since given the problems, there's a fair chance many of those who do try will be the sort of people to annoy other passengers). Far better to just ban them and avoid any possible risk (beyond that caused by the small number left on inadvertedly or intentionally) as well as any cost needed for testing. When they are providing a service to their customers, one which they're probably going to get paid for, that's a different matter. Nil Einne (talk) 12:49, 21 November 2012 (UTC)

In a general aviation aircraft, flying under the auspices of "Part 91," the pilot may permit you to use your cell phone if he/she believes it won't interfere with the aircraft operation: 14 CFR §91.21(b)5, prohibitions on operating a device do not apply to "Any other portable electronic device that the operator of the aircraft has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used." Aircraft operated for commercial passenger flights typically are conducted in compliance with much more stringent safety and legal regulations (Part 121), and numerous other restrictions imposed by the corporate office and its insurers. Aircraft operating outside the U.S. comply with other countries' safety regularions. On those flights, electronic devices may be prohibited for many reasons, including the fact that some devices do interfere with radio communication and navigation. If you'd like to try for yourself, place a mobile phone next to an airband scanner, and wait for a few minutes until you start hearing the clicking. It's sporadic, but it can audibly interfere with the VHF and UHF airband. This is only one of the more obvious types of interference phenomena, and it is easily demonstrable and repeatable in the safety of your home. Other more pathological types of interference also exist, and most pilots of commercial airlines do not enjoy testing their knowledge of RF circuit theory while operating large aircrafts. Nimur (talk) 13:19, 21 November 2012 (UTC)

For rules to work, rules need to be kept simple. Now imagine one person on an airliner is using a cellphone - not much of a problem. Now imagine all the passenger in a large airliner have their cellphones in use. To conserve battery energy, cellphones measure the incomming signal from the network. If the signal is strong (as it would be if you are close to a cellphone network site), the cellphone replies with a weak signal. If the network signal is weak (indicating your phone is far from the nearest network site) the phone responds by transmitting a strong signal. The aircraft may be on the limit of the range, so all cellphones transmit at full power - hundreds of them. And the metal skin of the aircract acts somewhat like the walls of a microwave oven (faraday cage) and keeps a lot of the energy within the plane. Not only might it interfere with aircraft systems, hundreds of cellphones all going at once at full power in a confined space could well be a health hazard. And, not the least important, you might not hear aircrew safety announcements. Note that cellphones when switched on communicate with teh network even when calls are not in progress.

Some airlines are investigating a means of allowing cellphones in flight. By using an onboard cell base, the phones can be instructed to use minimum power, and the onboard base relays to a telco ground station. There may be a method to restrict the number of cellphones in use, and breaking in with aircrew announcements. Floda 120.145.142.32 (talk) 13:21, 21 November 2012 (UTC)

A decade or two or three ago, some airlines (or maybe some types of planes) had telephones embedded in the seatback in front of you. You could place calls on them at any time. It wasn't cheap. It was several dollars a minute. But if you really, really needed to make a call, it was worth it. Does anyone know if any airlines or airplanes still use those? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:53, 21 November 2012 (UTC)

I've never heard of such a thing. But one time my flight was detoured to another airport and I was concerned about my elderly mother who was expecting me. I explained the problem to the hostess, and she said, no problem, the chief steward can radio ground and have your mother informed. And that's what they did. Another time I actually did really really need to make a call. I explained the situation to the hostess. She got permission from the captain, and then took me to a crew station and let me make the call from there. Great service from an Australian airline and there was no charge. Ratbone 60.228.252.120 (talk) 00:20, 22 November 2012 (UTC)

Naturally, wikipedia has information about it, embedded in the mobile phones on aircrafts article.[3] But it's good to know that there is a free phone available for must-call situations, at least on some airlines. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:13, 22 November 2012 (UTC)

I don't think it was there as a free phone intended for passenger use. I think it was there for crew operational use. It was a case of the crew providing excellent service by being flexible in meeting a need. Ratbone 120.145.15.193 (talk) 03:27, 22 November 2012 (UTC)

Our article sort of hints at this but these still exist on some/many? full service international airlines, potentially integrated to the remote control for the entertainment system (at least in economy). This is also mentioned in our In-flight entertainment article. As mentioned there, such systems now often provide SMS and perhaps email. I tried to use one such system for email or SMS on an Emirates flight about 1.5 years ago but it didn't seem to like my credit card so I gave up, IIRC it was about US$1 for an email or SMS which while expensive is the sort of thing I didn't mind paying for fun once. Of course the inclusion of picocells on planes as mention by me and others above is fairly similar including in some cases with very high rates [4], except allowing people to use their own devices and receive calls and SMSes although is perhaps having more success [5]. Nil Einne (talk) 05:55, 22 November 2012 (UTC)

Dot matrix printing on irregular surfaces

Please direct me to an image, or better yet, video showing how they get dot matrix printing (e.g., expiration/use-by dates) on such irregular surfaces as the sides of milk jugs (sometimes, even on the narrow handle) or juice bottles with embossed lettering or designs made in the bottle surface. If such labeling is actually printed on flat sheets of plastic before it is even formed in the bottle/jug forming machinery, please provide proof of that. Thanks. 20.137.2.50 (talk) 14:25, 21 November 2012 (UTC)

Inkjets used for labelling (often called "coding") have a long "throw distance" - the distance at which they can eject an ink stream and still produce a coherent image. This commercial coder has a throw distance of 90mm - so that allows you to label all kinds of things, without actually touching them. That allows printing on all kinds of complicated surface shapes, and printing on delicate things like eggs. A long throw coding printer is unlike an inkjet for printing on flat paper, which has a throw distance of a few mm. -- Finlay McWalterჷTalk 14:41, 21 November 2012 (UTC)

Although a lot of things that might appear to have been printed have in fact been inscribed with a laser (e.g.) It's common for plastic bottles to be inscribed this way, and in some cases packaging is made with a dual-layer panel ready for inscription - the laser burns off the top layer revealing the lower layer, which is of a contrasting colour. -- Finlay McWalterჷTalk 14:47, 21 November 2012 (UTC)

The article section Batch coding machine#Non contact coding type has a link to this video of an inkjet coding machine in operation. See also Laser engraving. Red Act (talk) 16:39, 21 November 2012 (UTC)

Thanks. What was the series of words you two typed into whatever search engine you used to arrive at the sources you did. Teach a man to fish? 20.137.2.50 (talk) 17:38, 21 November 2012 (UTC)

I started with the Inkjet printer article, which has a link to Batch coding machine in the "See also" section. And then the Batch coding machine article contains a link to Laser engraving (via the Laser marking redirect) in the "Non contact coding type" section. Red Act (talk) 18:49, 21 November 2012 (UTC)

Why are space probes so slow?

Why are space probes so slow? For example, the NASA webpage at http://voyager.jpl.nasa.gov/mission/fastfacts.html gives the speed of the Voyager probes as about 3 to 4 AU/year. That's a tiny fraction of the 173 AU/day of the speed of light. Given that nuclear reactors can operate for years without refueling in naval nuclear propulsion, why can't we just attach a nuclear reactor to a probe, and then have it continually accelerate the probe to around 99.9%+ of the speed of light? If we could do that, then with constant acceleration and deceleration, we'd be able to reach Alpha Centauri, 4.37 light-years away, in about 9 years, less than a decade! :) —SeekingAnswers (reply) 19:01, 21 November 2012 (UTC)

It is not that space probes are actually slow, they can be traveling at kilometers per second, it is that space is so big. Graeme Bartlett (talk) 20:37, 21 November 2012 (UTC)

Even with a nuclear reactor you get not to 99.9% The amount ov energy you need is more like 10 tonnes of antimater and 10 tonnes of matter and a conversion into acceleration than a spaceprobe with 10kg. You will cover the distance to Alpha Centauri in a few decades or hudreds of years. --Stone (talk) 20:46, 21 November 2012 (UTC)

Has anyone figured out the optimal speed that such an object could be pushed, to where it's pretty fast but doesn't burn out its fuel too soon and doesn't approach the light-speed-infinite-mass dilemma? Or maybe it's already doing that? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:49, 21 November 2012 (UTC)

It depends what you mean by "optimal". I imagine the obvious choice would be to optimise the ratio of acceleration over rate of fuel consumption, but I'm sure there are other definitions of "optimal" in this case (like travelling the maximum possible distance with a given amount of fuel). I may just be wrong and the two may be equal, but the question is very interesting indeed. -Anagogist (talk) 21:08, 21 November 2012 (UTC)

To use energy for propulsion one must also have reaction mass; one must propel some matter backwards in order to get a forward reaction. Submarines propel seawater, aircraft air, but a spacecraft in a vacuum has to carry, and expend, its own reaction mass. Various means of electrically powered spacecraft propulsion make efficient use of reaction mass. -- Finlay McWalterჷTalk 20:51, 21 November 2012 (UTC)

So then, how does nuclear pulse propulsion work? What is the reaction mass in that case? —SeekingAnswers (reply) 07:20, 22 November 2012 (UTC)

It is the nuclear material itself (the one in the bomb) --Lgriot (talk) 09:24, 22 November 2012 (UTC)

Space isn't a complete vacuum, though. Hence the Bussard ramjet idea. Of course, since it's not a complete vacuum, you also get drag and damage from the particles you hit, especially at near-light speeds. StuRat (talk) 01:06, 22 November 2012 (UTC)

There are a lot of concepts, but the ion propulsion took decades to come out of the lab. There is no big interest to go to Alpha Centauri if alot in the solar system is still to be done. A high speed probe into the Oort cloud might be the farthest we will go in the next generation. For that electric probulsion or solar sails or Electric sailmight be enough.--Stone (talk) 21:05, 21 November 2012 (UTC)

Volayer 2 says "sayonara" to the Solar System

• Even if the Voyager probes could have gone faster, their trajectories and hence their speed was geared towards visiting all the planets they could. Little point to go faster and not fly by anything interesting. μηδείς (talk) 21:25, 21 November 2012 (UTC)

Indeed. The purpose of the nuclear reactors on the Voyager probes isn't propulsion - it is to provide electircal power for scientific instruments, comms systems, gyroscopes etc. in deep space. Space probes carry very little propellant, and can only make small adjustments to their trajectories. Most of the time they are in free fall. Almost all of the kinetic energy of a space probe heading into the outer solar system comes not from their launch velocity or from their propulsion systems, but from gravity assist manoeuvres with planets - see chart on left of Voyager 2 speed v. distance from Sun. Cassini–Huygens had to make gravity assist manoeuvres around Venus (twice), Earth and Jupiter in order to reach Saturn. Gandalf61 (talk) 11:35, 22 November 2012 (UTC)

Is there a possiblity that these probes will eventually be captured by the sun's gravity and start to reverse course? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:14, 22 November 2012 (UTC)

Very, very unlikely. Voyager 1 and Voyager 2 are both travelling at speeds that are several times escape velocity for the Solar System. Unless one of them encounters some unknown agency that massively slows them down (black hole ? little green men ? eddies in the space time continuum ?) then they are not coming back. Gandalf61 (talk) 12:40, 22 November 2012 (UTC)

You forgot the most likely way for them to be recaptured by the Sun's gravity. Future humans may go grab them and put them in a museum, quite possibly on Earth. StuRat (talk) 06:22, 23 November 2012 (UTC)

That may be a decent candidate for most likely means for Voyager to return to the system, but it's still not very plausible in its own right. By the point at which we A) have the practical capability to retrieve the probe and B) we have the level of resources and capability to launch a deep-space mission for an errand of nostalgia, both Voyagers will fairly certainly have succumbed to the rigors of space travel. Even if some recognizable portions remain in-tact, finding them in the vastness of extra-solar space (even knowing their rough trajectories as they left the system) would be infeasible, even assuming the most fantastical technological advancements.

No, I'm afraid the only way we'll see one of these explorers again is if an alien species, against all odds, encounters one and decides to enhance it into a sentient being which then goes on to amass an inconceivable amount of knowledge and power while somehow lacking a clear conception of its own origins, generating confusion in the entity and urging it to return to Earth in a surreal quest to understand itself and fulfill its desire to complete its mission and reunite with its makers. Fingers crossed that it decides to make clones of our hottest women (for some reason) while it's at it -- baldness optional, V'Ger! Snow (talk) 09:18, 23 November 2012 (UTC)

Interesting point about not being able to find it. I wonder how large the uncertainty envelope is on it's location, and how easy such an object would be to find with RADAR or other technologies. Are there many other objects that size in the space between solar systems ? Enough to cause confusion ?

BTW, Star Trek: The Motion Picture had a major flaw, in that the Voyager probes wouldn't even have made it to the next solar system by that time, much less the far reaches of the galaxy. StuRat (talk) 15:21, 23 November 2012 (UTC)

That article reminded me of something I had forgotten; the probe is in fact neither Voyager 1 or Voyager 2 but rather Voyager 6, a speculative extension of the Voyager program that reflects the age of the movie. So who knows what it's capabilities were meant to be, though if it was meant to be a part of the same NASA program (which is obviously suggested by the remains of the original probe), I have a hard time imagining it was much of an upgrade compared to the types of interstellar travel prevalent in the franchise; certainly I'm sure it was meant to be subluminal. Without re-watching the movie and assuming accuracy in the plot summary of our article, it seems the explanation is that the machines that found the probe did so in nearby interstellar space and that amongst the upgrades they gave it was an increased rate of travel. Apparently though, "V'Ger" (the actual sentience) did not develop until some time after this during the probe's later travels. The alien-machine species that modified it was apparently racist though, as, despite being in the neighborhood, they didn't stop by our planet to edge us towards the ability to create submissive robot servants that look like Persis Khambatta... Snow (talk) 23:51, 24 November 2012 (UTC)

There are other practical concerns aside from fuel needs which limit the speed of any probe. For one, space in this little corner of the universe is hardly empty and the faster your probe is going, the more immediate its impact with something along its trajectory (and if the probe is going fast enough, a collusion with a tiny particle of space dust with no inertia of its own would be sufficient to obliterate the probe. And as the purpose of probes are to either collect data for our use or (conceivably) to make our existence known to other sentient beings, it makes more sense to have a slow moving probe that compromises on the distance it covers and the amount of time it can transmit information for any practical purpose. A probe traveling at anything remotely near the speed of light would be out of contact with us nearly instantaneously (and as noted above, likely vaporized almost as fast). All of which doesn't even take into account internal stresses of a craft traveling these speeds but made with our current understanding of materials science. For purely speculative purposes though, our Interstellar travel article does summarize some past proposed designs for constant-acceleration vessels. Snow (talk) 13:51, 22 November 2012 (UTC)

Vitamin K

Somewhere inthe recesses of my memory I recall hearing that the jewish people circumsized their sons on the 8th day because of the high level of Vitamin K at that time. Knowing that vitamin K is associated with coagulation - it seems plausible. But, is there something to vaidate this "memory"? Thanks! ---- — Preceding unsigned comment added by 24.153.163.210 (talk) 19:52, 21 November 2012 (UTC)

How would the ancients know about Vitamin K? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:47, 21 November 2012 (UTC)

I vagely remember it was the time of fastest blood clotting in the baby. Graeme Bartlett (talk) 21:00, 21 November 2012 (UTC)

That, they might know. It would be interesting to find out if that's the real reason, or if it's just a happy (so to speak) coincidence. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:28, 21 November 2012 (UTC)

• This PMID 11034761 high-quality study reflects the timing and biology, i.e. clearly supporting vitamin K deficiency as a usual risk for bleeding on days 1-7 of life (and it specifically mentions circumcision). This does not speak specifically to the traditional "knowledge" mentioned above. -- Scray (talk) 01:43, 22 November 2012 (UTC)

• One could just as easily speculate that circumcision seven days after birth is pre-historically related to the quarter lunation sacred to the pre-monotheistic Semitic moon goddess and the demon who walks by night who attacked Moses (requiring his wife to perform an emergency circumcision on him) on his wedding night. μηδείς (talk) 17:50, 22 November 2012 (UTC)

The ancients often had irrational explanations for their activities, but one expects them on average to avoid harm by a process of natural selection. Just as a bird's chromosomes don't need to know aeronautical engineering to fly, these ancient snippers didn't need to know the biology to obey it. Wnt (talk) 01:19, 23 November 2012 (UTC)

LED bulb

how can I light a led bulb by the ic 7403 on project board — Preceding unsigned comment added by 117.194.125.67 (talk) 19:57, 21 November 2012 (UTC)

quad 2-input NAND gate with open collector outputs, you will ahve to limit the current for the LED by using a suitable resister for the voltage in your circuit and the current required by the LED, else you may melt it. Graeme Bartlett (talk) 21:04, 21 November 2012 (UTC)

The LOW Level Output Current for the DM7403 is 16 mA max, so a resistor wouldn't be needed for normal LEDs (may not be so for all logical families), but the LED must be connected to the voltage source instead of the ground (anode to V+, cathode to output), and inputs must be high to drive the output low. The max current for high output is only 250 microAmp, not enough to drive the LED. I think this is the case for TTL in general. Ssscienccce (talk) 08:16, 22 November 2012 (UTC)

Carefull. If all 4 outputs are connected to the +ve rail, power dissipation may be such that the maximum chip temperature may be exceeded. In any case, the maximum allowable current sinked by an output, 30 mA, must be set by external circuitry (Page 3-4 of the Fairchild TTL Databook). It is good practice in any case to include a current limitting resistor. 220 ohms is a typical value for driving 3mm & 5mm diameter LEDs from the +5V rail. Keit 58.170.130.70 (talk) 11:43, 22 November 2012 (UTC)

I think we should also consider that the original question is about an "LED bulb", not (necessarily) a single LED. If the OP wants to switch a cluster of LEDs that make up a light bulb, some extra drive circuitry will be needed. Tevildo (talk) 21:53, 22 November 2012 (UTC)

UN hypocritical

This is the science reference desk. If you have a request for a reference we can help you. We cannot explain your personal political opinions
The following discussion has been closed. Please do not modify it.
Why does the UN condemn this http://www.bbc.co.uk/news/world-africa-20427549 but supports the Syrian rebels. I don't see much difference other than most of the syrian rebels are terrorists who came from Iraq, which the UN now wants to arm. --Wrk678 (talk) 22:29, 21 November 2012 (UTC) Self-explanatory closure. μηδείς (talk) 22:51, 21 November 2012 (UTC)

Broadleaf Evergreen Tree Identification

I'm trying to identify an evergreen tree in Virginia (U.S.) so I can buy some for my yard. It's a very large tree, but not particularly tall.

Here are some photos of a branch with leaves and another that shows a bud in detail, and an extreme close-up of a single leaf and how its veins align with the teeth.

The leaves are a deep green and glossy (like holly leaves) and simple with toothed margins (edges) but without the distinctive spines of holly leaves, and grow alternately along the branch from reddish stems. Leaves are about 4" long and 1" across at thickest point. The leaf buds are a deep red, with multiple petals. The bark is a very light brown.

Any ideas? The photos were taken today, and I don't know whether it has fruits and/or flowers at other times of the year. Thanks!

72.218.72.80 (talk) 23:31, 21 November 2012 (UTC)happyteatime

I think it's a rhododendron of some sort. Species-level ID will be much harder without more info (and especially flowers). Did you collect it from some park/woods, or someone's yard? There are native rhodo species in that region (e.g. rhododendron maximum is the state flower of WV), but there are also several horticultural varieties with different color and size blooms. Those buds at the tip are flower buds. They were set late summer, and will open next summer. Almost any local nursery will have a few different sizes and varieties available (finding the native at a nursery may be harder). If you have a few nice days left this season, right now would be a good time to plant, and you might be able to get them on sale as nurseries reduce their over-winter stock. SemanticMantis (talk) 00:11, 22 November 2012 (UTC)

It looks like rhododenron usually don't have teeth on the edges of the leaves, though? I saw this tree in someone's yard, so it may not be a native species. They had a bunch of these trees forming a wall alongside their house. When I say a wall, it really was like a wall-- the branches and leaves are tightly clustered together, and some of the lower branches almost touched the ground. The branches spread very far horizontally, but they weren't particularly tall -- maybe between five and eight feet tall. 72.218.72.80 (talk) 01:25, 22 November 2012 (UTC)happyteatime

The leaf reminds me very much of arbutus unedo, also known as the Strawberry Tree or madroño. I can't find any images of flower shoots before they are open. But they are largish bushes/small trees not high but wide, and evergreen. Here is an image of typical young bark, much rougher when older. They seem to be widely available in the US. Richard Avery (talk) 08:53, 22 November 2012 (UTC)

To me it looks like a Camellia, see also Camellia japonica. I adore them, but growing them to tree-size takes really long. Pardon my German (Fiiiisch!) (talk) 11:45, 23 November 2012 (UTC)

Custom weather warnings for UK?

Is there a service I can use to give notifications of low humidity for my city in the UK? I would like to use this condition when it arises (restricting notifications to particular times/days would be even better). — Preceding unsigned comment added by 78.144.193.174 (talk) 23:54, 21 November 2012 (UTC)

Can you explain a bit more ? Are you looking for warnings to pop up on your computer, text your mobile phone, or what ? Do you want it to warn you in advance or just when it happens ? In the latter case, an actual temperature and humidity probe would be the easiest way to go. I have two models, one with a battery-powered remote sensing unit, and one with a probe on a wire I thread out the window. Neither model has an audible alarm, but humidity can't drop all that quickly in the UK, so you could just check it periodically. StuRat (talk) 02:20, 22 November 2012 (UTC)

(Edit conflict) The BBC Weather site gives a recent humidity value rather than a forecast. I went to the page for Colchester, Essex and got the humidity reading for an hour previously. It's under the "Observations" heading at the bottom right of the page. Alansplodge (talk) 02:21, 22 November 2012 (UTC)

Weather.com seems to give forecasts in 15 minute increments, including humidity: [6]. StuRat (talk) 02:28, 22 November 2012 (UTC)

Yeah but none of those options notify me; they require me to monitor them. I would like a notification of either present or forecast low-humidity. 78.144.193.174 (talk) 22:30, 23 November 2012 (UTC)